2019 Vol. 36, No. 10
2019, 36(10): 2227-2234.
doi: 10.13801/j.cnki.fhclxb.20181114.001
Abstract:
This paper presents an analytical, finite element and experimental study on the mechanical behavior of thermoplastic carbon fiber reinforced polymer (CFRP) T-joint subjected to out-of-plane bending and bending-torsion coupling. The relationship between failure mode and load-displacement curve was analyzed. The analytical, finite element and experimental results were compared. In bending test, the stiffness discrepancies in analytical and finite element model compared to that in the experiment are 4.7% and 0.5%, respectively. In bending-torsion test, the stiffness discrepancies in analytical and finite element model compared to that in the experiment are 6.9% and 9.6%, respectively. The results in the experiment show that the progressive damage of CFRP laminate causes the damping of transverse bending stiffness of the T-joint. The T-joint begins to fail when the force reaches 2 047 N. The failure results include matrix cracking, matrix/fiber deboning of transverse fibers, delimitation and fiber breakage leading to transverse rupture.
This paper presents an analytical, finite element and experimental study on the mechanical behavior of thermoplastic carbon fiber reinforced polymer (CFRP) T-joint subjected to out-of-plane bending and bending-torsion coupling. The relationship between failure mode and load-displacement curve was analyzed. The analytical, finite element and experimental results were compared. In bending test, the stiffness discrepancies in analytical and finite element model compared to that in the experiment are 4.7% and 0.5%, respectively. In bending-torsion test, the stiffness discrepancies in analytical and finite element model compared to that in the experiment are 6.9% and 9.6%, respectively. The results in the experiment show that the progressive damage of CFRP laminate causes the damping of transverse bending stiffness of the T-joint. The T-joint begins to fail when the force reaches 2 047 N. The failure results include matrix cracking, matrix/fiber deboning of transverse fibers, delimitation and fiber breakage leading to transverse rupture.
2019, 36(10): 2235-2246.
doi: 10.13801/j.cnki.fhclxb.20181218.005
Abstract:
In order to investigate the bulletproof performance and failure mechanism of para-aromatic polyamide fiber/epoxy resin(EP) composite, the lead core projectiles were employed to penetrate composite target. The type of reinforcement was para-aromatic polyamide fiber, whereas the resin was EP; Nano-SiO2and polyvinyl butyral (PVB) worked as modifier. Unidirectional (UD) composites were fabricated using hot pressing process. The effects of single-layer fiber areal density, the structure of UD sheet, shooting angle and resin modification on the ballistic properties were discussed. The final fracture morphologies were observed by the stereomicroscopy. The failure mechanisms of composite target subjected to the ballistic impact were analyzed. The results show that para-aromatic polyamide fiber/EP composite exhibits excellent bulletproof performance. As the increasing of single-layer fiber areal density, the bulletproof performance of composite increases with fluctuations. Moreover, the bulletproof performances of 4 layer sheets with 0°/90°/0°/90° layer sequence(4UD) structures are superior to those of 2 layer sheets with 0°/90° layer sequence(2UD) structures. When shooting with a angle, the higher penetration layer ratio and smaller back face sign-ature (BFS) ratio are found. PVB improves the bulletproof performance. It can be concluded that the energy absorptions are significantly influenced by the tensile deformation of fiber, the delamination of sheet and the matrix resin cracking.
In order to investigate the bulletproof performance and failure mechanism of para-aromatic polyamide fiber/epoxy resin(EP) composite, the lead core projectiles were employed to penetrate composite target. The type of reinforcement was para-aromatic polyamide fiber, whereas the resin was EP; Nano-SiO2and polyvinyl butyral (PVB) worked as modifier. Unidirectional (UD) composites were fabricated using hot pressing process. The effects of single-layer fiber areal density, the structure of UD sheet, shooting angle and resin modification on the ballistic properties were discussed. The final fracture morphologies were observed by the stereomicroscopy. The failure mechanisms of composite target subjected to the ballistic impact were analyzed. The results show that para-aromatic polyamide fiber/EP composite exhibits excellent bulletproof performance. As the increasing of single-layer fiber areal density, the bulletproof performance of composite increases with fluctuations. Moreover, the bulletproof performances of 4 layer sheets with 0°/90°/0°/90° layer sequence(4UD) structures are superior to those of 2 layer sheets with 0°/90° layer sequence(2UD) structures. When shooting with a angle, the higher penetration layer ratio and smaller back face sign-ature (BFS) ratio are found. PVB improves the bulletproof performance. It can be concluded that the energy absorptions are significantly influenced by the tensile deformation of fiber, the delamination of sheet and the matrix resin cracking.
2019, 36(10): 2247-2258.
doi: 10.13801/j.cnki.fhclxb.20181119.004
Abstract:
To solve the problem of local electric field distortion caused by the difference in temperature gradient and material conductivity of DC cable accessory, copper calcium titanate (CaCu3Ti4O12) nanofibers were prepared by electrospinning and dispersed in liquid silicone rubber to synthesize CaCu3Ti4O12 nanofibers/liquid silicone rubber composites with nonlinear conductivity. The microstructures of CaCu3Ti4O12 nanofibers and CaCu3Ti4O12 nanofibers/liquid silicone rubber composites were characterized by XRD and SEM. The dielectric spectral characteristics, space charges characteristics and the conductivity and the breakdown strength in the environments of 30℃, 50℃ and 70℃ of the CaCu3Ti4O12 nanofibers/liquid silicone rubber composites were investigated. The intermediate joint of cable accessory model was established, and the simulation of the electric field distribution of the accessory was performed. The results show that the dielectric constant and conductivity of the composites increase with the increase of the content of CaCu3Ti4O12 nanofibers. When the nanofiber reaches 3vol%, the relative dielectric constant of the composite increases to 3.27 and the nonlinear conductivity has also changed by nearly 4 orders of magnitude. Then space charge test find that the dissipation of space charge is positively correlated with the content of CaCu3Ti4O12 nanofibers. The DC breakdown strength of the composites decreases with the increase of nanofiber content. The simulation analysis of the electric field distribution under the steady-state voltage shows that when the content of CaCu3Ti4O12 nanofiber is 2vol%, the maximum electric field strength at the root of the stress cone has been transferred from the reinforced insulation to the main insulation of the cable. Under the action of positive and negative polarity lightning impulse voltage, the maximum electric field strength of the 3vol% CaCu3Ti4O12 nanofibers/silicone rubber composite as the reinforced insulating material is far lower than its breakdown strength. The above experimental results show that the CaCu3Ti4O12 nanofibers as fillers have achieved the modification of the liquid silicone rubber at a lower doping concentration, which satisfies the electrical insulation performance requirement of the composite applied to the cable accessories.
To solve the problem of local electric field distortion caused by the difference in temperature gradient and material conductivity of DC cable accessory, copper calcium titanate (CaCu3Ti4O12) nanofibers were prepared by electrospinning and dispersed in liquid silicone rubber to synthesize CaCu3Ti4O12 nanofibers/liquid silicone rubber composites with nonlinear conductivity. The microstructures of CaCu3Ti4O12 nanofibers and CaCu3Ti4O12 nanofibers/liquid silicone rubber composites were characterized by XRD and SEM. The dielectric spectral characteristics, space charges characteristics and the conductivity and the breakdown strength in the environments of 30℃, 50℃ and 70℃ of the CaCu3Ti4O12 nanofibers/liquid silicone rubber composites were investigated. The intermediate joint of cable accessory model was established, and the simulation of the electric field distribution of the accessory was performed. The results show that the dielectric constant and conductivity of the composites increase with the increase of the content of CaCu3Ti4O12 nanofibers. When the nanofiber reaches 3vol%, the relative dielectric constant of the composite increases to 3.27 and the nonlinear conductivity has also changed by nearly 4 orders of magnitude. Then space charge test find that the dissipation of space charge is positively correlated with the content of CaCu3Ti4O12 nanofibers. The DC breakdown strength of the composites decreases with the increase of nanofiber content. The simulation analysis of the electric field distribution under the steady-state voltage shows that when the content of CaCu3Ti4O12 nanofiber is 2vol%, the maximum electric field strength at the root of the stress cone has been transferred from the reinforced insulation to the main insulation of the cable. Under the action of positive and negative polarity lightning impulse voltage, the maximum electric field strength of the 3vol% CaCu3Ti4O12 nanofibers/silicone rubber composite as the reinforced insulating material is far lower than its breakdown strength. The above experimental results show that the CaCu3Ti4O12 nanofibers as fillers have achieved the modification of the liquid silicone rubber at a lower doping concentration, which satisfies the electrical insulation performance requirement of the composite applied to the cable accessories.
2019, 36(10): 2259-2265.
doi: 10.13801/j.cnki.fhclxb.20190522.001
Abstract:
The combinations of cerium phenylphosphonate (CeHPP) and decabromodiphenyl oxide (DBDPO) were used for flame retardancy of glass fiber reinforced poly(ethylene terephthalate)(GF/PET) composites by using melt blending. Thermograviment analysis(TGA) was employed to investigate the thermal decomposition behavior of the flame retardant DBDPO-CeHPP-GF/PET composites. The combustion properties of DBDPO-CeHPP-GF/PET composites were measured by using limiting oxygen index (LOI), underwriters laboratories 94 (UL-94) and microscale combustion calorimeter (MCC). SEM was used to investigate the microtopography of char residues of DBDPO-CeHPP-GF/PET composites. The thermal properties and flame retardance of DBDPO-CeHPP-GF/PET composites are significantly improved by the incorporation of the combinations of CeHPP and DBDPO. For DBDPO-CeHPP-GF/PET composite with mass ratio of GF/PET composites:DBDPO:CeHPP of 91:6:3, the UL-94 V-0 classification and high LOI (29.5%) are achieved. The total heat release (THR), peak heat release rate (PHRR) and heat release capacity (HRC) of DBDPO-CeHPP-GF/PET composites at this ratio are respectively reduced by 10.2%, 13.1% and 12.8% comparing with the pure GF/PET composites. And the flame retardant mechanism of DBDPO-CeHPP-GF/PET composites was analyzed based on the SEM results of char residues.
The combinations of cerium phenylphosphonate (CeHPP) and decabromodiphenyl oxide (DBDPO) were used for flame retardancy of glass fiber reinforced poly(ethylene terephthalate)(GF/PET) composites by using melt blending. Thermograviment analysis(TGA) was employed to investigate the thermal decomposition behavior of the flame retardant DBDPO-CeHPP-GF/PET composites. The combustion properties of DBDPO-CeHPP-GF/PET composites were measured by using limiting oxygen index (LOI), underwriters laboratories 94 (UL-94) and microscale combustion calorimeter (MCC). SEM was used to investigate the microtopography of char residues of DBDPO-CeHPP-GF/PET composites. The thermal properties and flame retardance of DBDPO-CeHPP-GF/PET composites are significantly improved by the incorporation of the combinations of CeHPP and DBDPO. For DBDPO-CeHPP-GF/PET composite with mass ratio of GF/PET composites:DBDPO:CeHPP of 91:6:3, the UL-94 V-0 classification and high LOI (29.5%) are achieved. The total heat release (THR), peak heat release rate (PHRR) and heat release capacity (HRC) of DBDPO-CeHPP-GF/PET composites at this ratio are respectively reduced by 10.2%, 13.1% and 12.8% comparing with the pure GF/PET composites. And the flame retardant mechanism of DBDPO-CeHPP-GF/PET composites was analyzed based on the SEM results of char residues.
2019, 36(10): 2266-2274.
doi: 10.13801/j.cnki.fhclxb.20181114.002
Abstract:
Fiber Bragg grating(FBG) sensors were embedded in triangle region of carbon fiber reinforced epoxy composite T-stiffened panels to real-time monitor the strain change during impact. By embedding the FBG sensors in the composite laminates and triangle region of the T-stiffened composite plates respectively, the effects of FBG sensors on the properties of the composite laminates and T-stiffened composite plates were studied. The results show that the tensile strength of the composite laminates with FBG sensors can be about 5% lower than the laminates without FBG sensors. Within the failure strain scope of FBG sensors, the FBG sensors could accurately monitor the strain signals real-time for the composite laminates. The compressive load of the T-stiffened panels with FBG sensors in triangle area is almost same as the T-stiffened panels without FBG sensors. Moreover, the effects of impact location and impact energy on the impact time and max-strain measured by the FBG sensors were studied. The results show that the impact time is increased with increasing impact energy. However, the max-strain is decreased with increasing impact distance, increased with increasing impact energy. By embedding the FBG sensors in triangle area of the composite T-stiffened panels, the impact location and impact energy of the composite T-stiffened panels could be monitored real-time by FBG sensors preliminarily.
Fiber Bragg grating(FBG) sensors were embedded in triangle region of carbon fiber reinforced epoxy composite T-stiffened panels to real-time monitor the strain change during impact. By embedding the FBG sensors in the composite laminates and triangle region of the T-stiffened composite plates respectively, the effects of FBG sensors on the properties of the composite laminates and T-stiffened composite plates were studied. The results show that the tensile strength of the composite laminates with FBG sensors can be about 5% lower than the laminates without FBG sensors. Within the failure strain scope of FBG sensors, the FBG sensors could accurately monitor the strain signals real-time for the composite laminates. The compressive load of the T-stiffened panels with FBG sensors in triangle area is almost same as the T-stiffened panels without FBG sensors. Moreover, the effects of impact location and impact energy on the impact time and max-strain measured by the FBG sensors were studied. The results show that the impact time is increased with increasing impact energy. However, the max-strain is decreased with increasing impact distance, increased with increasing impact energy. By embedding the FBG sensors in triangle area of the composite T-stiffened panels, the impact location and impact energy of the composite T-stiffened panels could be monitored real-time by FBG sensors preliminarily.
2019, 36(10): 2275-2285.
doi: 10.13801/j.cnki.fhclxb.20190103.002
Abstract:
Based on the linear three-dimensional elastic theory and Kelvin-Voigt model, the wave equation of longitudinal guided waves in the viscoelastic anisotropic hollow cylinder was derived by using the Legendre polynomial expansion method, and the decoupled wave equation was solved numerically while the implications of the related equations were fully expounded. In order to validate our program, the dispersion curves and attenuation curves of the viscoelastic hollow cylinder with a large ratio of radius to thickness were calculated in comparison with the available date. Meanwhile, the displacement distribution and stress distribution were further calculated for the reliability of the method. Then, the influence of the ratio of radius to thickness and the effect of viscous constants were investigated respectively, which contains the dispersion curves and attenuation curves of longitudinal modes and torsional ones. The effects of viscoelastic parameters to the torsional waves were illustrated.
Based on the linear three-dimensional elastic theory and Kelvin-Voigt model, the wave equation of longitudinal guided waves in the viscoelastic anisotropic hollow cylinder was derived by using the Legendre polynomial expansion method, and the decoupled wave equation was solved numerically while the implications of the related equations were fully expounded. In order to validate our program, the dispersion curves and attenuation curves of the viscoelastic hollow cylinder with a large ratio of radius to thickness were calculated in comparison with the available date. Meanwhile, the displacement distribution and stress distribution were further calculated for the reliability of the method. Then, the influence of the ratio of radius to thickness and the effect of viscous constants were investigated respectively, which contains the dispersion curves and attenuation curves of longitudinal modes and torsional ones. The effects of viscoelastic parameters to the torsional waves were illustrated.
2019, 36(10): 2286-2293.
doi: 10.13801/j.cnki.fhclxb.20190226.002
Abstract:
In order to explore the failure analysis of composite laminates, a numerical model based on Puck failure criterion was established. For Puck's inter-fiber fracture failure theory, the traversing search method and the partition golden section search method (PGSS) were used to predict the angle of fracture surface under different stress states. The computational accuracy and efficiency of the two algorithms were also analyzed. Research shows that the PGSS method has high search accuracy and efficiency. The proposed algorithm was implemented using ABAQUS-VUMAT subroutines and numerical analysis was performed for G23 out-of-plane shear tests of composite laminates. By comparison with the experimental results about the load-displacement curves, DIC strain field and failure mode under transverse (G23) shear load, it has been verified that the current model works well in predicting the structural response and structural failure mode.
In order to explore the failure analysis of composite laminates, a numerical model based on Puck failure criterion was established. For Puck's inter-fiber fracture failure theory, the traversing search method and the partition golden section search method (PGSS) were used to predict the angle of fracture surface under different stress states. The computational accuracy and efficiency of the two algorithms were also analyzed. Research shows that the PGSS method has high search accuracy and efficiency. The proposed algorithm was implemented using ABAQUS-VUMAT subroutines and numerical analysis was performed for G23 out-of-plane shear tests of composite laminates. By comparison with the experimental results about the load-displacement curves, DIC strain field and failure mode under transverse (G23) shear load, it has been verified that the current model works well in predicting the structural response and structural failure mode.
2019, 36(10): 2294-2301.
doi: 10.13801/j.cnki.fhclxb.20190104.003
Abstract:
The interference-fit joint can improve the bearing capacity and sealing performance of carbon fiber reinforced epoxy resin composite (CFRP). However, the oversized thrust force will cause bending deflection and delamination, which severely impacts the safety of the products. The assembling process of CFRP laminates with interference-fit joint, such as drilling, installing and tightening, was analyzed. The interference-fit bolt installation process of CFRP laminates was divided into 4 stages. The mechanical behavior of each stage was analyzed in detail. The extrusion force and friction at the bolt bar and chamfer were modeled. The thrust force of the whole installation process was established based on the displacement boundary condition and stages. The interference-fit bolt installation process of CFRP laminates was experimented and simulated by ABAQUS, the radial stress distribution and thrust force curves were compared and analyzed. The results of the analytical model and simulation and experiment match well. This work lays the foundation for the study of joint delamination and optimization.
The interference-fit joint can improve the bearing capacity and sealing performance of carbon fiber reinforced epoxy resin composite (CFRP). However, the oversized thrust force will cause bending deflection and delamination, which severely impacts the safety of the products. The assembling process of CFRP laminates with interference-fit joint, such as drilling, installing and tightening, was analyzed. The interference-fit bolt installation process of CFRP laminates was divided into 4 stages. The mechanical behavior of each stage was analyzed in detail. The extrusion force and friction at the bolt bar and chamfer were modeled. The thrust force of the whole installation process was established based on the displacement boundary condition and stages. The interference-fit bolt installation process of CFRP laminates was experimented and simulated by ABAQUS, the radial stress distribution and thrust force curves were compared and analyzed. The results of the analytical model and simulation and experiment match well. This work lays the foundation for the study of joint delamination and optimization.
2019, 36(10): 2302-2307.
doi: 10.13801/j.cnki.fhclxb.20190221.001
Abstract:
In order to understand the macroscopic mechanical properties and experimental phenomena of propellants from the mechanism, it is necessary to carry out meso-mechanical research on propellants, and the representative volume element (RVE) is an important part of meso-mechanics research. Based on the random sequential adsorption (RSA) method, the delivery area was discretized into a background grid, and then a second random delivery was performed, which can generate a mesoscopic model with 80vol% particle volume fraction, and the model generation efficiency is also improved compared with the traditional RSA method. The method was programmed in Python language, and the secondary development interface of ABAQUS was used to realize the rapid generation of RVE model and load periodic boundary conditions. The numerical examples were used to illustrate the effectiveness of the algorithm, which provides a reference for the meso-analysis of propellants.
In order to understand the macroscopic mechanical properties and experimental phenomena of propellants from the mechanism, it is necessary to carry out meso-mechanical research on propellants, and the representative volume element (RVE) is an important part of meso-mechanics research. Based on the random sequential adsorption (RSA) method, the delivery area was discretized into a background grid, and then a second random delivery was performed, which can generate a mesoscopic model with 80vol% particle volume fraction, and the model generation efficiency is also improved compared with the traditional RSA method. The method was programmed in Python language, and the secondary development interface of ABAQUS was used to realize the rapid generation of RVE model and load periodic boundary conditions. The numerical examples were used to illustrate the effectiveness of the algorithm, which provides a reference for the meso-analysis of propellants.
2019, 36(10): 2308-2315.
doi: 10.13801/j.cnki.fhclxb.20181217.002
Abstract:
Based on the software ABAQUS, the strength prediction model of carbon fiber reinforced polymer(CFRP)-aluminum bonded-bolted hybrid double-lap joint was built and simulation analysis was carried out. Comparing with the test result, the failure modes and the carrying capacity of the joint were studied under the tensile load condition. It is shown that the adhesive joint can be reinforced with the load-sharing of the bolt. The hybrid joint firstly suffers the fracture failure of the adhesive and reaches the final failure when the bearing failure appears near the hole. The carrying capacity of the joint predicted by the model has the error value of 9.7%, which illustrates good consistency with the test result. This method can offer some references for the analysis and design of the composite-metal bonded-bolted hybrid joints.
Based on the software ABAQUS, the strength prediction model of carbon fiber reinforced polymer(CFRP)-aluminum bonded-bolted hybrid double-lap joint was built and simulation analysis was carried out. Comparing with the test result, the failure modes and the carrying capacity of the joint were studied under the tensile load condition. It is shown that the adhesive joint can be reinforced with the load-sharing of the bolt. The hybrid joint firstly suffers the fracture failure of the adhesive and reaches the final failure when the bearing failure appears near the hole. The carrying capacity of the joint predicted by the model has the error value of 9.7%, which illustrates good consistency with the test result. This method can offer some references for the analysis and design of the composite-metal bonded-bolted hybrid joints.
2019, 36(10): 2316-2329.
doi: 10.13801/j.cnki.fhclxb.20181119.006
Abstract:
Effect of the vibrating boundary condition on resistance of shape memory alloy (SMA)-glass fiber/epoxy resin composites subjected to low-velocity impact was investigated by finite element method (FEM). Hashin's failure criterion and Brinson's model were implemented into FEM to characterize the constitutive relations of glass fiber/epoxy resin laminates and SMA, respectively. Fixed boundary condition was maintained in simulation to verify the accuracy of material parameters and procedures by comparing with impact experiment of SMA-glass fiber/epoxy resin composite. A series of vibrating boundaries with amplitudes were applied during the simulation process to reveal the effect on impact resistances. The simulation results indicate that the impact resistance of the composite without SMA under large amplitude is lower than that under small amplitude; as for SMA-glass fiber/epoxy resin composite, the impact resistance is higher.
Effect of the vibrating boundary condition on resistance of shape memory alloy (SMA)-glass fiber/epoxy resin composites subjected to low-velocity impact was investigated by finite element method (FEM). Hashin's failure criterion and Brinson's model were implemented into FEM to characterize the constitutive relations of glass fiber/epoxy resin laminates and SMA, respectively. Fixed boundary condition was maintained in simulation to verify the accuracy of material parameters and procedures by comparing with impact experiment of SMA-glass fiber/epoxy resin composite. A series of vibrating boundaries with amplitudes were applied during the simulation process to reveal the effect on impact resistances. The simulation results indicate that the impact resistance of the composite without SMA under large amplitude is lower than that under small amplitude; as for SMA-glass fiber/epoxy resin composite, the impact resistance is higher.
2019, 36(10): 2330-2340.
doi: 10.13801/j.cnki.fhclxb.20181116.001
Abstract:
Epoxy resin is widely used as electronic packaging material with many excellent performances, however, the internal stress of epoxy resin induced in the curing process will bring about unfavorable influence on packaged products. Many experiments were carried out to research the performance parameters of epoxy resin used to electronic packaging, such as curing kinetics, density, thermal conductivity, glass transition temperature, elastic modulus, chemical shrinkage strain, thermal strain, etc. After that, mathematic models of these parameters in the curing process were established. Three-dimensional finite element model was established with ABAQUS to simulate the temperature field, curing degree field, stress and strain field of epoxy resin in the curing process. Sequentially coupled analysis was used to perform heat conduction analysis and stress-strain analysis successively in ABAQUS. The fiber Bragg grating(FBG) experiment was carried out to monitor the evolution of temperature and strain in epoxy resin during the curing process. Comparison of the results between experiment and simulation demonstrates that the finite element model established in this paper is of high reliability.
Epoxy resin is widely used as electronic packaging material with many excellent performances, however, the internal stress of epoxy resin induced in the curing process will bring about unfavorable influence on packaged products. Many experiments were carried out to research the performance parameters of epoxy resin used to electronic packaging, such as curing kinetics, density, thermal conductivity, glass transition temperature, elastic modulus, chemical shrinkage strain, thermal strain, etc. After that, mathematic models of these parameters in the curing process were established. Three-dimensional finite element model was established with ABAQUS to simulate the temperature field, curing degree field, stress and strain field of epoxy resin in the curing process. Sequentially coupled analysis was used to perform heat conduction analysis and stress-strain analysis successively in ABAQUS. The fiber Bragg grating(FBG) experiment was carried out to monitor the evolution of temperature and strain in epoxy resin during the curing process. Comparison of the results between experiment and simulation demonstrates that the finite element model established in this paper is of high reliability.
2019, 36(10): 2341-2347.
doi: 10.13801/j.cnki.fhclxb.20181109.001
Abstract:
Hydroxyapatite (HA) reinforced WE43 magnesium composites (HA/WE43) were prepared by friction stir processing (FSP), the influence of rotation speed on HA distribution and the changes of microstructure and mechanical properties before and after FSP were studied. The microstructure of HA/WE43 composites was characterized by optical microscope, SEM and TEM, and the microhardness and tensile properties tests were conducted to evaluate the mechanical properties. The results show that the grain size of HA/WE43 composites is significantly finer than that of the base materials. During the processing, the presence of HA particles enhances the grain refinement effect of FSP. HA particles tend to cluster in the HA/WE43 composites prepared at a relatively low rotation speed. As the rotation speed increases, the HA particles distribute more uniform and the agglomeration phenomenon is improved. Although locally agglomerated HA particles can become the origin of cracks in the composite during tensile deformation, an improvement of ultimate tensile strength, yield strength and elongation is achieved in the HA/WE43 composites.
Hydroxyapatite (HA) reinforced WE43 magnesium composites (HA/WE43) were prepared by friction stir processing (FSP), the influence of rotation speed on HA distribution and the changes of microstructure and mechanical properties before and after FSP were studied. The microstructure of HA/WE43 composites was characterized by optical microscope, SEM and TEM, and the microhardness and tensile properties tests were conducted to evaluate the mechanical properties. The results show that the grain size of HA/WE43 composites is significantly finer than that of the base materials. During the processing, the presence of HA particles enhances the grain refinement effect of FSP. HA particles tend to cluster in the HA/WE43 composites prepared at a relatively low rotation speed. As the rotation speed increases, the HA particles distribute more uniform and the agglomeration phenomenon is improved. Although locally agglomerated HA particles can become the origin of cracks in the composite during tensile deformation, an improvement of ultimate tensile strength, yield strength and elongation is achieved in the HA/WE43 composites.
2019, 36(10): 2348-2356.
doi: 10.13801/j.cnki.fhclxb.20190226.001
Abstract:
Copper matrix composites reinforced with single sized TiB2 particles and mixing sized TiB2 particles were prepared by powder metallurgy, respectively. Effects of mixing sized TiB2 particles (2 μm+50 μm) on the friction behavior under non-current and current of the TiB2/Cu composites were studied. Microstructure observation shows that the different TiB2 particles are evenly distributed in the copper matrix. The higher relative density, the hardness and electrical conductivity of mixing sized TiB2/Cu composite are obviously better than those of TiB2/Cu composites reinforced with single sized TiB2 particles. The results of friction and wear tests show that:The friction and wear properties of mixing sized TiB2/Cu composites are significantly higher than those of single sized TiB2/Cu composites. When the mixed ratio of 2 μm and 50 μm TiB2 particles is 1:2, the TiB2/Cu composite has the best wear resistance, when the current is 0 A, compared to the composites with 2 μm single sized, its friction coefficient and wear rate decrease by 17.3% and 62.5%, respectively, when the current is 25 A, compared to TiB2/Cu composites with 2 μm single sized, its friction coefficient and wear rate decrease by 6% and 45.8%, respectively. Meanwhile, its wear surface is more flat and the stability of the current carrying and efficiency of the current carrying capacity are obviously improved. The analysis of wear mechanism shows that:The mixed TiB2 particles are favorable for improving the current carrying quality of TiB2/Cu composites. The mixed TiB2 particles play a supporting role in the friction process, and the small TiB2 particles disperse and strengthen the Cu matrix. The synergistic effect of that makes the TiB2/Cu composites have better current-carrying friction and wear resistance.
Copper matrix composites reinforced with single sized TiB2 particles and mixing sized TiB2 particles were prepared by powder metallurgy, respectively. Effects of mixing sized TiB2 particles (2 μm+50 μm) on the friction behavior under non-current and current of the TiB2/Cu composites were studied. Microstructure observation shows that the different TiB2 particles are evenly distributed in the copper matrix. The higher relative density, the hardness and electrical conductivity of mixing sized TiB2/Cu composite are obviously better than those of TiB2/Cu composites reinforced with single sized TiB2 particles. The results of friction and wear tests show that:The friction and wear properties of mixing sized TiB2/Cu composites are significantly higher than those of single sized TiB2/Cu composites. When the mixed ratio of 2 μm and 50 μm TiB2 particles is 1:2, the TiB2/Cu composite has the best wear resistance, when the current is 0 A, compared to the composites with 2 μm single sized, its friction coefficient and wear rate decrease by 17.3% and 62.5%, respectively, when the current is 25 A, compared to TiB2/Cu composites with 2 μm single sized, its friction coefficient and wear rate decrease by 6% and 45.8%, respectively. Meanwhile, its wear surface is more flat and the stability of the current carrying and efficiency of the current carrying capacity are obviously improved. The analysis of wear mechanism shows that:The mixed TiB2 particles are favorable for improving the current carrying quality of TiB2/Cu composites. The mixed TiB2 particles play a supporting role in the friction process, and the small TiB2 particles disperse and strengthen the Cu matrix. The synergistic effect of that makes the TiB2/Cu composites have better current-carrying friction and wear resistance.
2019, 36(10): 2357-2363.
doi: 10.13801/j.cnki.fhclxb.20181218.004
Abstract:
The surface of graphite flakes(GFs) was coated with Si by salt bath method, and the graphite flakes/Al composites (Si-GFs/Al) were prepared by vacuum hot pressing method. 10vol% Cu mesh was added to Si-GFs/Al composites, and the effects of Cu mesh on thermal conductivity and mechanical properties were studied. The microstructure and micro interface of Si-GFs/Al composites were characterized by SEM, focusing ion beam (FIB) and TEM. The fracture mechanism of the composites was analyzed. The results show that highly clustered GFs bands have been built in the Si-GFs/Al composites after Cu mesh added. When the GFs volume fraction is 30vol%~40vol%, the thermal conductivity of Si-GFs/Al composites increases by about 20%, and the bending strength increases by more than 40%. The thermal conductivity and bending strength of Si-GFs/Al composites with 40vol% GFs both reach a satisfactory value, which are 512 W/(mK) and 127 MPa, respectively.
The surface of graphite flakes(GFs) was coated with Si by salt bath method, and the graphite flakes/Al composites (Si-GFs/Al) were prepared by vacuum hot pressing method. 10vol% Cu mesh was added to Si-GFs/Al composites, and the effects of Cu mesh on thermal conductivity and mechanical properties were studied. The microstructure and micro interface of Si-GFs/Al composites were characterized by SEM, focusing ion beam (FIB) and TEM. The fracture mechanism of the composites was analyzed. The results show that highly clustered GFs bands have been built in the Si-GFs/Al composites after Cu mesh added. When the GFs volume fraction is 30vol%~40vol%, the thermal conductivity of Si-GFs/Al composites increases by about 20%, and the bending strength increases by more than 40%. The thermal conductivity and bending strength of Si-GFs/Al composites with 40vol% GFs both reach a satisfactory value, which are 512 W/(mK) and 127 MPa, respectively.
2019, 36(10): 2364-2370.
doi: 10.13801/j.cnki.fhclxb.20181128.001
Abstract:
Polypyrrole(PPy)/polydopamine(PDA) coating was prepared on the surface of 7075 aluminum alloy through electrochemical polymerization to improve the corrosion resistance of aluminum alloy organic coatings. FE-SEM, atomic force microscope and FTIR were used to analyze the surface morphology, surface roughness and chemical composition of PPy/PDA coating, respectively. AC impedance spectroscopy was applied to study the impedance characteristics of the coating. The polarization voltage and polarization current of the aluminum alloy coated with PPy/PDA were analyzed by polarization curves to study the corrosion resistance. The research shows that pyrrole and dopamine simultaneously electrochemically polymerize on the aluminum alloy surface by one-step electrochemical polymerization. PPy molecular chains and PDA molecular chains form network interpenetrating structure. PPy/PDA coating has a sea-island structure with a surface roughness of (73.740±7.811) nm, which is close to the roughness of the pure PPy coating (74.582±7.227) nm. The polarization curves indicate that the corrosion current and corrosion voltages of the coated PPy/PDA coating are 4.1825×10-6 Acm-2 and -0.6919 V, respectively. And the corrosion current and corrosion voltages of the pure PPy are 7.618×10-6 Acm-2 and -0.7403 V, respectively.
Polypyrrole(PPy)/polydopamine(PDA) coating was prepared on the surface of 7075 aluminum alloy through electrochemical polymerization to improve the corrosion resistance of aluminum alloy organic coatings. FE-SEM, atomic force microscope and FTIR were used to analyze the surface morphology, surface roughness and chemical composition of PPy/PDA coating, respectively. AC impedance spectroscopy was applied to study the impedance characteristics of the coating. The polarization voltage and polarization current of the aluminum alloy coated with PPy/PDA were analyzed by polarization curves to study the corrosion resistance. The research shows that pyrrole and dopamine simultaneously electrochemically polymerize on the aluminum alloy surface by one-step electrochemical polymerization. PPy molecular chains and PDA molecular chains form network interpenetrating structure. PPy/PDA coating has a sea-island structure with a surface roughness of (73.740±7.811) nm, which is close to the roughness of the pure PPy coating (74.582±7.227) nm. The polarization curves indicate that the corrosion current and corrosion voltages of the coated PPy/PDA coating are 4.1825×10-6 Acm-2 and -0.6919 V, respectively. And the corrosion current and corrosion voltages of the pure PPy are 7.618×10-6 Acm-2 and -0.7403 V, respectively.
2019, 36(10): 2371-2379.
doi: 10.13801/j.cnki.fhclxb.20190103.001
Abstract:
Reaction melt infiltration (RMI) was adopted to prepare ZrC-SiC/(C/C) composites with a density of 3.288 g/cm3. The analysis methods such as SEM-EDS, XRD and TEM were used to discuss the microstructure of ZrC-SiC/(C/C) composites. The results show that the ceramic phase has been fully and uniformly filled in the matrices of C/C composites, whose internal structure mainly consists of ZrC, SiC, pyrolytic carbon(PyC) and carbon fiber(CF). The infiltrant reacted fully and no residual metals Zr and Si were detected in the composites. The ablation properties of ZrC-SiC/(C/C) composites were determined at 2 500℃ after ablation for 30 s, 60 s and 90 s with the oxyacetylene ablation equipment. The mass ablation rates are 5.667 mg/s, 2.907 mg/s and 3.030 mg/s and the linear ablation rates are 1.001 μm/s, 4.662 μm/s and 4.450 μm/s. Test ablation results show that the ceramic phase in the ablation center of ZrC-SiC/(C/C) composites is gradually oxidized to produce ZrO2 and SiO2 during the high-temperature ablation. The resulting binary glassy mixture protects and fills the ablation pores of the composites, so as to avoid the occurrence of oxidation reaction in the composites and improve the ablation properties of such materials effectively.
Reaction melt infiltration (RMI) was adopted to prepare ZrC-SiC/(C/C) composites with a density of 3.288 g/cm3. The analysis methods such as SEM-EDS, XRD and TEM were used to discuss the microstructure of ZrC-SiC/(C/C) composites. The results show that the ceramic phase has been fully and uniformly filled in the matrices of C/C composites, whose internal structure mainly consists of ZrC, SiC, pyrolytic carbon(PyC) and carbon fiber(CF). The infiltrant reacted fully and no residual metals Zr and Si were detected in the composites. The ablation properties of ZrC-SiC/(C/C) composites were determined at 2 500℃ after ablation for 30 s, 60 s and 90 s with the oxyacetylene ablation equipment. The mass ablation rates are 5.667 mg/s, 2.907 mg/s and 3.030 mg/s and the linear ablation rates are 1.001 μm/s, 4.662 μm/s and 4.450 μm/s. Test ablation results show that the ceramic phase in the ablation center of ZrC-SiC/(C/C) composites is gradually oxidized to produce ZrO2 and SiO2 during the high-temperature ablation. The resulting binary glassy mixture protects and fills the ablation pores of the composites, so as to avoid the occurrence of oxidation reaction in the composites and improve the ablation properties of such materials effectively.
2019, 36(10): 2380-2388.
doi: 10.13801/j.cnki.fhclxb.20181112.001
Abstract:
Continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have good application prospects in the nuclear engineering structures, due to their excellent high-temperature mechanical properties, irradiation stability and low helium permeability. Understanding the damage evolution mechanism and the strength is significant for the application of SiC/SiC composites. Based on the multi-scale characteristics of the fabrication process and component material distribution of plain woven SiC/SiC composites, fiber-scale (the fiber yarn model) and yarn-scale (the woven fabric model) unit cell models were established considering the local periodicity of the microstructure of the composites. In this paper, finite element method was applied to predict the elastic properties and strength properties of the fiber-scale model, which were then substituted into the yarn-scale model. The Tsai-Wu failure criterion was employed and the stiffness reduction was conducted in the failed elements according to the different failure modes. The progressive damage process of plain woven SiC/SiC composites under uniaxial tensile load was simulated. The numerical simulation curve is in good agreement with the experimental curve, which demonstrates the predictive capability of the proposed method for predicting the strength of plain woven SiC/SiC composites.
Continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have good application prospects in the nuclear engineering structures, due to their excellent high-temperature mechanical properties, irradiation stability and low helium permeability. Understanding the damage evolution mechanism and the strength is significant for the application of SiC/SiC composites. Based on the multi-scale characteristics of the fabrication process and component material distribution of plain woven SiC/SiC composites, fiber-scale (the fiber yarn model) and yarn-scale (the woven fabric model) unit cell models were established considering the local periodicity of the microstructure of the composites. In this paper, finite element method was applied to predict the elastic properties and strength properties of the fiber-scale model, which were then substituted into the yarn-scale model. The Tsai-Wu failure criterion was employed and the stiffness reduction was conducted in the failed elements according to the different failure modes. The progressive damage process of plain woven SiC/SiC composites under uniaxial tensile load was simulated. The numerical simulation curve is in good agreement with the experimental curve, which demonstrates the predictive capability of the proposed method for predicting the strength of plain woven SiC/SiC composites.
2019, 36(10): 2389-2397.
doi: 10.13801/j.cnki.fhclxb.20181119.005
Abstract:
With Na-montmorillonite as the research object, mixture of cetyl trimethyl ammonium bromide and absolute ethyl alcohol, mixture of silane coupling agent KH550 and absolute ethyl alcohol as modifier to prepare compound modified Na-montmorillonite, compound modified Na-montmorillonite/rubber composites were prepared by accelerant, sulfur, zinc oxide, stearic acid, rubber and carbon black partially substituted by compound modified Na-montmorillonite. The preparation process parameters of compound modified Na-montmorillonite/rubber composites were optimized by radial basis function(RBF) neural network, compound modified Na-montmorillonite and compound modified Na-montmorillonite/rubber composites were tested and characterized. The results show that RBF neural network of reinforcement properties and the flame retardant property of compound modified Na-montmorillonite/rubber composites have the best approximation effect when "spread coeficient" is 0.50-0.65. Compound modified Na-montmorillonite/rubber composites show good reinforcement properties and flame retardant property (tensile strength of 19.1 MPa, tear strength of 43.5 kN/m and limit oxygen index of 32.83%) when the amount of deionized water is 1 074 g, amount of cetyl trimethyl ammonium bromide is 13.7 g, amount of absolute ethyl alcohol is 14.8 g, amount of silane coupling agent KH550 is 0.32 g and stirring rate is 2 890 r/min.
With Na-montmorillonite as the research object, mixture of cetyl trimethyl ammonium bromide and absolute ethyl alcohol, mixture of silane coupling agent KH550 and absolute ethyl alcohol as modifier to prepare compound modified Na-montmorillonite, compound modified Na-montmorillonite/rubber composites were prepared by accelerant, sulfur, zinc oxide, stearic acid, rubber and carbon black partially substituted by compound modified Na-montmorillonite. The preparation process parameters of compound modified Na-montmorillonite/rubber composites were optimized by radial basis function(RBF) neural network, compound modified Na-montmorillonite and compound modified Na-montmorillonite/rubber composites were tested and characterized. The results show that RBF neural network of reinforcement properties and the flame retardant property of compound modified Na-montmorillonite/rubber composites have the best approximation effect when "spread coeficient" is 0.50-0.65. Compound modified Na-montmorillonite/rubber composites show good reinforcement properties and flame retardant property (tensile strength of 19.1 MPa, tear strength of 43.5 kN/m and limit oxygen index of 32.83%) when the amount of deionized water is 1 074 g, amount of cetyl trimethyl ammonium bromide is 13.7 g, amount of absolute ethyl alcohol is 14.8 g, amount of silane coupling agent KH550 is 0.32 g and stirring rate is 2 890 r/min.
2019, 36(10): 2398-2406.
doi: 10.13801/j.cnki.fhclxb.20190301.001
Abstract:
Natural biology has evolved over millions of years and has formed near-perfect structure. Study on the structure of natural biomaterials is the basis of bionic research. The microstructural features of the shell of Hyriopsis cumingii, including the stratum corneum, prismatic layer, nacre, the interface between them and the topographys of trip-like crystal ribbon were described by using the SEM and AFM. The shape and size of the aragonite platelets and the dimensional change between the layers were measured according to the observations. The results show that there exist cracks in the stratum corneum. There is no obvious transition interface between the nacre and the prismatic layer. The structural defects of strip-like crystal ribbon are found in the nacre. The thickness of the whole shell and nacre increases first increases and then decreases along the 0 growth line, while the thickness of the monolayer aragonite tablet is uneven. The thickest part of the platelet can be more than twice as the thinnest part. The structure of the Hyriopsis cumingii was studied further, which provides a theoretical basis for its excellent mechanical properties, and provides new directions for the future bionic structure design.
Natural biology has evolved over millions of years and has formed near-perfect structure. Study on the structure of natural biomaterials is the basis of bionic research. The microstructural features of the shell of Hyriopsis cumingii, including the stratum corneum, prismatic layer, nacre, the interface between them and the topographys of trip-like crystal ribbon were described by using the SEM and AFM. The shape and size of the aragonite platelets and the dimensional change between the layers were measured according to the observations. The results show that there exist cracks in the stratum corneum. There is no obvious transition interface between the nacre and the prismatic layer. The structural defects of strip-like crystal ribbon are found in the nacre. The thickness of the whole shell and nacre increases first increases and then decreases along the 0 growth line, while the thickness of the monolayer aragonite tablet is uneven. The thickest part of the platelet can be more than twice as the thinnest part. The structure of the Hyriopsis cumingii was studied further, which provides a theoretical basis for its excellent mechanical properties, and provides new directions for the future bionic structure design.
2019, 36(10): 2407-2417.
doi: 10.13801/j.cnki.fhclxb.20181108.007
Abstract:
The strength characteristics of materials composed of polymer curing agent(PCA)-basalt fiber(BF)/sand composite were deeply studied by uniaxial compression test, direct shear test and direct tensile test, the effects of polymer curing agent content, basalt fiber content (mass ratio to dry sand) and sand density on the strength of the composites were compared and analyzed. And the strength enhancement mechanism of PCA-BF/Sand was analyzed based on the results of the tests and SEM images. The test results show that:The compressive strength, shear strength and tensile strength of PCA-BF/Sand are obviously enhanced after mixed with basalt fiber and polymer curing agent, and the residual compressive strength increases with the increase of content of polymer curing agent. With the increase of the content of basalt fiber and the polymer curing agent, the strength of PCA-BF/Sand increases rapidly first, and when the polymer curing agent content and the fiber content reach 3% and 0.6%, the increase is slowed down. With the increase of PCA-BF/Sand density, the compressive strength and shear strength of the composites have been increased, and the tensile strength decreases first and then increases and then decreases and reaches maximum at a density of 1.55 g/cm3. With evaporation of water, polymer curing agent formed space network between sand particles, therefore, scattered sand were connected with each other to become an integral whole, and the basalt fiber added into sand can play a reinforcing role in the sand, thereby the strength of PCA-BF/Sand composite was effectively improved.
The strength characteristics of materials composed of polymer curing agent(PCA)-basalt fiber(BF)/sand composite were deeply studied by uniaxial compression test, direct shear test and direct tensile test, the effects of polymer curing agent content, basalt fiber content (mass ratio to dry sand) and sand density on the strength of the composites were compared and analyzed. And the strength enhancement mechanism of PCA-BF/Sand was analyzed based on the results of the tests and SEM images. The test results show that:The compressive strength, shear strength and tensile strength of PCA-BF/Sand are obviously enhanced after mixed with basalt fiber and polymer curing agent, and the residual compressive strength increases with the increase of content of polymer curing agent. With the increase of the content of basalt fiber and the polymer curing agent, the strength of PCA-BF/Sand increases rapidly first, and when the polymer curing agent content and the fiber content reach 3% and 0.6%, the increase is slowed down. With the increase of PCA-BF/Sand density, the compressive strength and shear strength of the composites have been increased, and the tensile strength decreases first and then increases and then decreases and reaches maximum at a density of 1.55 g/cm3. With evaporation of water, polymer curing agent formed space network between sand particles, therefore, scattered sand were connected with each other to become an integral whole, and the basalt fiber added into sand can play a reinforcing role in the sand, thereby the strength of PCA-BF/Sand composite was effectively improved.
2019, 36(10): 2418-2425.
doi: 10.13801/j.cnki.fhclxb.20190118.002
Abstract:
Low-dimensional semiconductor materials have attracted wide attention and research due to their extraordinary physical properties. In this paper, metal organic chemical vapor deposition (MOCVD) was used to grow InAs/GaAs radial heterostructure nanowires using gold as catalysts. The effects of growth temperatures of InAs radial heterostructure on the morphology and crystal structure of the nanowires were discussed. Increasing the growth temperature of InAs material can effectively inhibit the axial growth of nanowires and achieve the growth of radial heterostructures. The lateral crystal surface rotation occurs when the heterostructure nanowires grow laterally, which is the result of the lower side of the nanowires. The research work in this paper provides a theoretical basis and scientific basis for the development of micro-nano technology.
Low-dimensional semiconductor materials have attracted wide attention and research due to their extraordinary physical properties. In this paper, metal organic chemical vapor deposition (MOCVD) was used to grow InAs/GaAs radial heterostructure nanowires using gold as catalysts. The effects of growth temperatures of InAs radial heterostructure on the morphology and crystal structure of the nanowires were discussed. Increasing the growth temperature of InAs material can effectively inhibit the axial growth of nanowires and achieve the growth of radial heterostructures. The lateral crystal surface rotation occurs when the heterostructure nanowires grow laterally, which is the result of the lower side of the nanowires. The research work in this paper provides a theoretical basis and scientific basis for the development of micro-nano technology.
2019, 36(10): 2426-2438.
doi: 10.13801/j.cnki.fhclxb.20181228.001
Abstract:
The large eccentric compression behavior of coral aggregate reinforced concrete column (CA/CC) with different types of reinforcement and concrete strength grade was tested. The failure mode, deformation and bearing capacity were investigated. The relationships of load-displacement and load-strain were established. The applicable calculation model for ultimate bearing capacity (Nu) of CA/CC under large eccentric compression was suggested. The results show that the compression behavior of CA/CC is similar to the ordinary aggregate reinforced concrete column (OA/CC). With the increase of concrete strength grade, the load corresponding to the sudden change of the strain of CA/CC longitudinal tensile steel gradually increases. In the loading process, a greater slip was produced in the layer between the organic new coated steel and coral aggregate concrete(CA/C). Nu of common steel is approximately 7.1%~20.8% higher than that of organic new coated steel. The application of organic new coated steel in the CA/C structure is suggested to effectively inhibit steel corrosion and extends the effective service life of the CA/C structure. Based on the comprehensive consideration on the effects of steel corrosion and slip of the coated steel, a calculation model for Nu of CA/CC under large eccentric compression is proposed.
The large eccentric compression behavior of coral aggregate reinforced concrete column (CA/CC) with different types of reinforcement and concrete strength grade was tested. The failure mode, deformation and bearing capacity were investigated. The relationships of load-displacement and load-strain were established. The applicable calculation model for ultimate bearing capacity (Nu) of CA/CC under large eccentric compression was suggested. The results show that the compression behavior of CA/CC is similar to the ordinary aggregate reinforced concrete column (OA/CC). With the increase of concrete strength grade, the load corresponding to the sudden change of the strain of CA/CC longitudinal tensile steel gradually increases. In the loading process, a greater slip was produced in the layer between the organic new coated steel and coral aggregate concrete(CA/C). Nu of common steel is approximately 7.1%~20.8% higher than that of organic new coated steel. The application of organic new coated steel in the CA/C structure is suggested to effectively inhibit steel corrosion and extends the effective service life of the CA/C structure. Based on the comprehensive consideration on the effects of steel corrosion and slip of the coated steel, a calculation model for Nu of CA/CC under large eccentric compression is proposed.
2019, 36(10): 2439-2447.
doi: 10.13801/j.cnki.fhclxb.20181218.003
Abstract:
Through the disc splitting testing, the exact crack width of concrete has been prefabricated. In this work, the effects of steel fiber(SF) and macro polypropylene(PP) fiber on tortuosity, recovery rate and damage of concrete cracks were studied. The crack widths at different locations were measured using the digital microscope (Supereyes) and Image Pro Plus (an image processing software). In order to analyze the relationship between ultrasonic velocity and crack width as well as damage variable factors of different specimens, the ultrasonic velocity passing through the concrete disc under splitting load was also measured. The experimental results show that the crack widening can be controlled by the fiber bridging effect, and the crack recovery and tortuosity of crack can be increased simultaneously. Compared with the concrete sample with a SF content of 25 kg/m3, the crack tortuosity of the sample with a SF content of 55 kg/m3 increases by 26.9%; the hybrid use of macro PP fibers and SF indicates significant positive hybrid effect on the increasing of crack surface tortuosity. The steel fibers acrossing the cracks may improve the propagation of ultrasonic wave and decline the loss of the ultrasonic velocity. The ultrasonic velocity may decrease with the increasing of the crack width, and there is an exponential relationship between the crack width and ultrasonic velocity, which can be used to illustrate the crack development of concrete matrix.
Through the disc splitting testing, the exact crack width of concrete has been prefabricated. In this work, the effects of steel fiber(SF) and macro polypropylene(PP) fiber on tortuosity, recovery rate and damage of concrete cracks were studied. The crack widths at different locations were measured using the digital microscope (Supereyes) and Image Pro Plus (an image processing software). In order to analyze the relationship between ultrasonic velocity and crack width as well as damage variable factors of different specimens, the ultrasonic velocity passing through the concrete disc under splitting load was also measured. The experimental results show that the crack widening can be controlled by the fiber bridging effect, and the crack recovery and tortuosity of crack can be increased simultaneously. Compared with the concrete sample with a SF content of 25 kg/m3, the crack tortuosity of the sample with a SF content of 55 kg/m3 increases by 26.9%; the hybrid use of macro PP fibers and SF indicates significant positive hybrid effect on the increasing of crack surface tortuosity. The steel fibers acrossing the cracks may improve the propagation of ultrasonic wave and decline the loss of the ultrasonic velocity. The ultrasonic velocity may decrease with the increasing of the crack width, and there is an exponential relationship between the crack width and ultrasonic velocity, which can be used to illustrate the crack development of concrete matrix.
2019, 36(10): 2448-2457.
doi: 10.13801/j.cnki.fhclxb.20181210.001
Abstract:
Thermal protection structures (TPS) are key structures for reusable space vehicles, whose safety and maintainability are of vital importance. There are very few researches on structural health monitoring for TPS, especially for C/C, C/SiC composite TPS. The structural health monitoring method based on active elastic wave was studied for the C/C TPS of reusable space vehicles. A numerical simulation method of TPS elastic wave was proposed. On the basis of verifying the effectiveness of the method, the elastic wave propagation characteristics for C/C TPS structural damage monitoring were studied. From signal time domain characteristics, elastic wave propagation wave field, damage scattering signal, damage scattering signal wave field and damage index, analyzing the elastic wave propagation characteristics of C/C TPS and the effects of damage were analyzed completely. The results show that when the length of the stratified damage edge is greater than 25 mm, the damage index changes dramatically, so the structural health monitoring method based on elastic wave can be used to monitor the internal stratified damage and damage expansion of C/C TPS.
Thermal protection structures (TPS) are key structures for reusable space vehicles, whose safety and maintainability are of vital importance. There are very few researches on structural health monitoring for TPS, especially for C/C, C/SiC composite TPS. The structural health monitoring method based on active elastic wave was studied for the C/C TPS of reusable space vehicles. A numerical simulation method of TPS elastic wave was proposed. On the basis of verifying the effectiveness of the method, the elastic wave propagation characteristics for C/C TPS structural damage monitoring were studied. From signal time domain characteristics, elastic wave propagation wave field, damage scattering signal, damage scattering signal wave field and damage index, analyzing the elastic wave propagation characteristics of C/C TPS and the effects of damage were analyzed completely. The results show that when the length of the stratified damage edge is greater than 25 mm, the damage index changes dramatically, so the structural health monitoring method based on elastic wave can be used to monitor the internal stratified damage and damage expansion of C/C TPS.
2019, 36(10): 2458-2468.
doi: 10.13801/j.cnki.fhclxb.20190510.002
Abstract:
The slow-freeze-thaw cycle test was carried out on 72 nano carbon fiber/concrete specimens with 6 different nano-carbon fiber contents, the effects of nano-carbon fiber content on the anti-freezing performance of nano carbon fiber/concrete were studied by measuring the anti-flaking ability, mass loss rate, relative dynamic elastic modulus and compressive strength loss rate of nano carbon fiber/concrete after different freeze-thaw cycles. In addition, with the help of FE-SEM electron microscopy and mercury intrusion test, the improvement mechanism of nano-carbon fiber on the anti-freezing performance of concrete were analyzed from the microscopic level. The results show that nano carbon fiber can improve the frost resistance of concrete by improving the micro-morphology of concrete, refining its pore structure, improving its integrity and compactness, and improving the frost resistance of concrete. When the content of nano carbon fiber is 3vol%, the anti-freezing performance of concrete is optimized. Compared with ordinary concrete, after 300 freeze-thaw cycles, the relative dynamic elastic modulus of nano carbon fiber/concrete increases by 33.2%, and the anti-flaking ability is significantly enhanced. Under the same number of freeze-thaw cycles, with the increase of nano carbon fiber content, the relative dynamic modulus and compressive strength loss rate of nano carbon fiber/concrete shows a trend of increasing first and then decreasing, and the mass loss rate shows a trend of decreasing first and then increasing. However, when the nano carbon fiber content is up to 5vol%, the frost resistance of nano carbon fiber/concrete is still better than that of ordinary concrete, and the more the number of freeze-thaw cycles, the more significant the effect of nano carbon fiber on the antifreeze performance of concrete.
The slow-freeze-thaw cycle test was carried out on 72 nano carbon fiber/concrete specimens with 6 different nano-carbon fiber contents, the effects of nano-carbon fiber content on the anti-freezing performance of nano carbon fiber/concrete were studied by measuring the anti-flaking ability, mass loss rate, relative dynamic elastic modulus and compressive strength loss rate of nano carbon fiber/concrete after different freeze-thaw cycles. In addition, with the help of FE-SEM electron microscopy and mercury intrusion test, the improvement mechanism of nano-carbon fiber on the anti-freezing performance of concrete were analyzed from the microscopic level. The results show that nano carbon fiber can improve the frost resistance of concrete by improving the micro-morphology of concrete, refining its pore structure, improving its integrity and compactness, and improving the frost resistance of concrete. When the content of nano carbon fiber is 3vol%, the anti-freezing performance of concrete is optimized. Compared with ordinary concrete, after 300 freeze-thaw cycles, the relative dynamic elastic modulus of nano carbon fiber/concrete increases by 33.2%, and the anti-flaking ability is significantly enhanced. Under the same number of freeze-thaw cycles, with the increase of nano carbon fiber content, the relative dynamic modulus and compressive strength loss rate of nano carbon fiber/concrete shows a trend of increasing first and then decreasing, and the mass loss rate shows a trend of decreasing first and then increasing. However, when the nano carbon fiber content is up to 5vol%, the frost resistance of nano carbon fiber/concrete is still better than that of ordinary concrete, and the more the number of freeze-thaw cycles, the more significant the effect of nano carbon fiber on the antifreeze performance of concrete.
2019, 36(10): 2469-2477.
doi: 10.13801/j.cnki.fhclxb.20181129.001
Abstract:
Glass fiber reinforced polymer composites(GFRP) has high strength, good heat resistance and strong resistance to alkaline corrosion, and has been widely used in the field of civil engineering. In order to study the interfacial friction characteristics between the silty soil in the Yellow River flooding area and GFRP cloth, the direct shear friction test was carried out by using TZY-1 geosynthetic material comprehensive tester, and the effects of moisture content, compactness, normal stress on the interface friction characteristics were analyzed. The results show that the interfacial frictional strength of silty soil and GFRP cloth increases with the increase of compaction degree; the interfacial friction strength reaches the maximum when the soil moisture content is the optimal moisture content, and decreases when it exceeds the optimal moisture content; the interfacial shear resistance increases with the increase of normal stress, and the friction coefficient decreases with the increase of normal stress.
Glass fiber reinforced polymer composites(GFRP) has high strength, good heat resistance and strong resistance to alkaline corrosion, and has been widely used in the field of civil engineering. In order to study the interfacial friction characteristics between the silty soil in the Yellow River flooding area and GFRP cloth, the direct shear friction test was carried out by using TZY-1 geosynthetic material comprehensive tester, and the effects of moisture content, compactness, normal stress on the interface friction characteristics were analyzed. The results show that the interfacial frictional strength of silty soil and GFRP cloth increases with the increase of compaction degree; the interfacial friction strength reaches the maximum when the soil moisture content is the optimal moisture content, and decreases when it exceeds the optimal moisture content; the interfacial shear resistance increases with the increase of normal stress, and the friction coefficient decreases with the increase of normal stress.
2019, 36(10): 2478-2485.
doi: 10.13801/j.cnki.fhclxb.20181218.001
Abstract:
Fiber reinforced polymer (FRP)-steel composite circular tube confined concrete has been studied extensively in recent years due to its excellent comprehensive properties, however, a complete computational model to predict the stress-strain curve is still lacking. On the basis of the author's existing research results, the axial compression test results of 96 FRP-steel composite circular tube confined concrete columns were extensively collected and the influence rule of specimen parameters was systematically analyzed, a complete calculation model of stress-strain curve of FRP-steel composite circular tube confined concrete was presented, including the calculation methods of peak stress, peak strain, ultimate stress and ultimate strain, and the prediction model of the whole stress-strain curve was proposed. The model can predict the characteristics of the stress-strain curve of FRP-steel composite circular tube confined concrete, and the predicted results are in good agreement with the test results. The proposed model has good universality and accuracy.
Fiber reinforced polymer (FRP)-steel composite circular tube confined concrete has been studied extensively in recent years due to its excellent comprehensive properties, however, a complete computational model to predict the stress-strain curve is still lacking. On the basis of the author's existing research results, the axial compression test results of 96 FRP-steel composite circular tube confined concrete columns were extensively collected and the influence rule of specimen parameters was systematically analyzed, a complete calculation model of stress-strain curve of FRP-steel composite circular tube confined concrete was presented, including the calculation methods of peak stress, peak strain, ultimate stress and ultimate strain, and the prediction model of the whole stress-strain curve was proposed. The model can predict the characteristics of the stress-strain curve of FRP-steel composite circular tube confined concrete, and the predicted results are in good agreement with the test results. The proposed model has good universality and accuracy.
