2020 Vol. 37, No. 2
2020, 37(2): 237-241.
doi: 10.13801/j.cnki.fhclxb.20190929.001
Abstract:
Plainification' is regarded as a promising design methodology for metallic materials to decrease the degree of alloying and reduce the difficulty of recycling. In this paper, we introduced the idea of planification into composites and proposed the concept of plainified composites, in which multiscale structural design methods (i.e. interface engineering, defect engineering) were adopted to improve the properties and optimize the overall performance of composites. Without changing the composition of composites or increasing the filler volume fraction, the tunability of materials was fully explored and expanded by multiscale design methods. Based on a canonical composite system, the possibility, advantages and expected results of making composites plainified were demonstrated. The various design methods that could be applied to achieve plainified composites were also illustrated. The application of this design methodology was exemplified in carbon nanotube(CNT)/silicone elastomer(SE) composites through interface engineering towards a plainified composite absorber.
Plainification' is regarded as a promising design methodology for metallic materials to decrease the degree of alloying and reduce the difficulty of recycling. In this paper, we introduced the idea of planification into composites and proposed the concept of plainified composites, in which multiscale structural design methods (i.e. interface engineering, defect engineering) were adopted to improve the properties and optimize the overall performance of composites. Without changing the composition of composites or increasing the filler volume fraction, the tunability of materials was fully explored and expanded by multiscale design methods. Based on a canonical composite system, the possibility, advantages and expected results of making composites plainified were demonstrated. The various design methods that could be applied to achieve plainified composites were also illustrated. The application of this design methodology was exemplified in carbon nanotube(CNT)/silicone elastomer(SE) composites through interface engineering towards a plainified composite absorber.
2020, 37(2): 242-251.
doi: 10.13801/j.cnki.fhclxb.20190509.001
Abstract:
The 3D graphene-multi walled carbon nanotube/thermoplastic polyurethane (GA-MWCNTs/TPU) composites were prepared using 3D graphene-multi walled carbon nanotubes aerogels (GA-MWCNTs) and thermoplastic polyurethane (TPU). GA-MWCNTs was prepared by hydrothermal reduction method for grafting carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) onto graphene oxide (GO) and then freeze-drying. Subsequently, the filling TPU was impregnated the GA-MWCNTs in a vacuum state to obtain the GA-MWCNTs/TPU composite. The chemical structure and microstructure of GA-MWCNTs were characterized by means of FTIR, Raman, XPS, TEM and SEM, then MWCNTs-COOH mass fraction effect on the GA-MWCNTs/TPU composite performance was analyzed by means of TGA-DSC, resistance measuring instrument and mechanical testing machine. The results demonstrate that MWCNTs-COOH can cross-linking and support the GO inter-lamellar structures, forming a honeycomb 3D network structure with a pore size of about 1.2 mm. When the mass fraction of MWCNTs-COOH (using 120 mg GO as reference) is 10wt%, the electrical conductivity, thermal stability and mechanical properties of GA-MWCNTs/TPU composite are greatly improved. Compared with the GA/TPU, the volume resistivity of GA-MWCNTs/TPU composite reduces by 63.0%, thermal decomposition temperature increases by 7℃, and the stress at 30% strain increases by 8.2%.
The 3D graphene-multi walled carbon nanotube/thermoplastic polyurethane (GA-MWCNTs/TPU) composites were prepared using 3D graphene-multi walled carbon nanotubes aerogels (GA-MWCNTs) and thermoplastic polyurethane (TPU). GA-MWCNTs was prepared by hydrothermal reduction method for grafting carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) onto graphene oxide (GO) and then freeze-drying. Subsequently, the filling TPU was impregnated the GA-MWCNTs in a vacuum state to obtain the GA-MWCNTs/TPU composite. The chemical structure and microstructure of GA-MWCNTs were characterized by means of FTIR, Raman, XPS, TEM and SEM, then MWCNTs-COOH mass fraction effect on the GA-MWCNTs/TPU composite performance was analyzed by means of TGA-DSC, resistance measuring instrument and mechanical testing machine. The results demonstrate that MWCNTs-COOH can cross-linking and support the GO inter-lamellar structures, forming a honeycomb 3D network structure with a pore size of about 1.2 mm. When the mass fraction of MWCNTs-COOH (using 120 mg GO as reference) is 10wt%, the electrical conductivity, thermal stability and mechanical properties of GA-MWCNTs/TPU composite are greatly improved. Compared with the GA/TPU, the volume resistivity of GA-MWCNTs/TPU composite reduces by 63.0%, thermal decomposition temperature increases by 7℃, and the stress at 30% strain increases by 8.2%.
2020, 37(2): 252-259.
doi: 10.13801/j.cnki.fhclxb.20190513.001
Abstract:
In order to study the effect of nano clay modification on the mechanical properties of composites, the 3D orthogonal glass fiber woven fabric reinforced nano clay modification epoxy resin composites were manufactured by vacuum assisted resin transfer molding (VARTM) process. The bending and tensile properties of the composite modified with different mass fractions (1wt%, 2wt%, 3wt%, 4wt%) of nano clay in 0° and 90° directions were tested respectively. The results show that the composite with the nano clay fraction of 1wt% has the highest bending strength and stiffness. And the bending strength in 0° and 90° directions have been increased by 7.21% and 13.71%, respectively. The bending modulus have been increased by 5.69% and 16.64%, respectively. In addition, the composite modified with 3wt% nano clay has the best tensile properties. For the 0° and 90° directions, the corresponding tensile strength have been increased by 24.96% and 27.93%, respectively. And the tensile modules have been increased by 21.35% and 13.26%, respectively. Due to the contact area increase between fibers and epoxy resin, the interface bonding strength has been increased as nano clay is dispersed in the matrix in a nano scale layered form, the mechanical performance of the composite has been improved significantly.
In order to study the effect of nano clay modification on the mechanical properties of composites, the 3D orthogonal glass fiber woven fabric reinforced nano clay modification epoxy resin composites were manufactured by vacuum assisted resin transfer molding (VARTM) process. The bending and tensile properties of the composite modified with different mass fractions (1wt%, 2wt%, 3wt%, 4wt%) of nano clay in 0° and 90° directions were tested respectively. The results show that the composite with the nano clay fraction of 1wt% has the highest bending strength and stiffness. And the bending strength in 0° and 90° directions have been increased by 7.21% and 13.71%, respectively. The bending modulus have been increased by 5.69% and 16.64%, respectively. In addition, the composite modified with 3wt% nano clay has the best tensile properties. For the 0° and 90° directions, the corresponding tensile strength have been increased by 24.96% and 27.93%, respectively. And the tensile modules have been increased by 21.35% and 13.26%, respectively. Due to the contact area increase between fibers and epoxy resin, the interface bonding strength has been increased as nano clay is dispersed in the matrix in a nano scale layered form, the mechanical performance of the composite has been improved significantly.
2020, 37(2): 260-266.
doi: 10.13801/j.cnki.fhclxb.20190509.002
Abstract:
The layer-by-layer of self assembly (LBL) method was adopted to construct CH-APP flame retardant coating by alternating adsorption of cationic chitosan (CH) and anionic ammonium polyphosphate (APP) on the surface of sisal fiber cellulose microcrystal (SFCM), and (CH-APP)n/SFCM flame retardant composites were prepared. The structure and properties of the (CH-APP)n/SFCM composites were measured by Zeta potential analyzer, FTIR, TGA, POM, vertical flame testing (VFT), SEM. The results of Zeta potential show the surface of SFCM potential is positive and negative in the alternately adsorption process, which indicates the CH-APP coating is successfully coated on the surface of SFCM. POM and SEM reveal a thick coating was covered on the surface of the SFCM by LBL and the surface of SFCM becomes more rough. With the increase of the number of CH-APP self assembled layers, the initial decomposition temperature(T5%) of (CH-APP)n/SFCM composite reduces from 279.4℃ to 243.1℃, and the char residue of (CH-APP)n/SFCM composite increases from 11.24% to 32.06%. The results of VFT show that (CH-APP)n/SFCM composites present outstanding flame retardancy after LBL method and the (CH-APP)n/SFCM composite with 10 layers assembled exhibits the best flame retardancy with self-extinguishing fire flame retardant.
The layer-by-layer of self assembly (LBL) method was adopted to construct CH-APP flame retardant coating by alternating adsorption of cationic chitosan (CH) and anionic ammonium polyphosphate (APP) on the surface of sisal fiber cellulose microcrystal (SFCM), and (CH-APP)n/SFCM flame retardant composites were prepared. The structure and properties of the (CH-APP)n/SFCM composites were measured by Zeta potential analyzer, FTIR, TGA, POM, vertical flame testing (VFT), SEM. The results of Zeta potential show the surface of SFCM potential is positive and negative in the alternately adsorption process, which indicates the CH-APP coating is successfully coated on the surface of SFCM. POM and SEM reveal a thick coating was covered on the surface of the SFCM by LBL and the surface of SFCM becomes more rough. With the increase of the number of CH-APP self assembled layers, the initial decomposition temperature(T5%) of (CH-APP)n/SFCM composite reduces from 279.4℃ to 243.1℃, and the char residue of (CH-APP)n/SFCM composite increases from 11.24% to 32.06%. The results of VFT show that (CH-APP)n/SFCM composites present outstanding flame retardancy after LBL method and the (CH-APP)n/SFCM composite with 10 layers assembled exhibits the best flame retardancy with self-extinguishing fire flame retardant.
2020, 37(2): 267-275.
doi: 10.13801/j.cnki.fhclxb.20190419.001
Abstract:
Research on the parameters of structural strength is essential for composite structural design. However, the effects of structural size on strength under different hygrothermal environments have been less investigated. Numerical and experimental methods were adopted to study the influence of humidity, temperature and width to diameter ratio(W/D) on T800/X850 carbon fiber reinforced epoxy resin composite (CF/EP) open-hole laminates compression strength. The parameters of the research specimens were designed, and results of the open-hole composite laminates compression failure under different hygrothermal environments were obtained by the tests. A progressive damage model was established to analyse the effects of humidity, temperature and geometric parameters on composite laminates compression strength by using the existing progressive damage methods of composites considering the influence of hygrothermal environments. The good consistency between the numerical and experimental results validates the model. Combined with the experimental and numerical analysis, the influence law of the parameters was revealed. The research shows that hygrothermal environments has a significant effect on compression failure loads of T800/X850 CF/EP open-hole laminates. Compared with the room temperature and dry(RTD) conditions, the room temperature and wet(RTW) conditions and the elevated temperature and wet(ETW) conditions compressive failure loads are reduced by 7.75% and 14.68%, respectively. The failure modes under RTW conditions and RTD conditions are close to each other. The failure modes of ETW conditions are different and the failure area is larger. The compressive failure strength increases with the increase of the W/D in RTW conditions and RTD conditions, and the rates of growth are similar. The rate of growth in ETW conditions increases slower than the former two.
Research on the parameters of structural strength is essential for composite structural design. However, the effects of structural size on strength under different hygrothermal environments have been less investigated. Numerical and experimental methods were adopted to study the influence of humidity, temperature and width to diameter ratio(W/D) on T800/X850 carbon fiber reinforced epoxy resin composite (CF/EP) open-hole laminates compression strength. The parameters of the research specimens were designed, and results of the open-hole composite laminates compression failure under different hygrothermal environments were obtained by the tests. A progressive damage model was established to analyse the effects of humidity, temperature and geometric parameters on composite laminates compression strength by using the existing progressive damage methods of composites considering the influence of hygrothermal environments. The good consistency between the numerical and experimental results validates the model. Combined with the experimental and numerical analysis, the influence law of the parameters was revealed. The research shows that hygrothermal environments has a significant effect on compression failure loads of T800/X850 CF/EP open-hole laminates. Compared with the room temperature and dry(RTD) conditions, the room temperature and wet(RTW) conditions and the elevated temperature and wet(ETW) conditions compressive failure loads are reduced by 7.75% and 14.68%, respectively. The failure modes under RTW conditions and RTD conditions are close to each other. The failure modes of ETW conditions are different and the failure area is larger. The compressive failure strength increases with the increase of the W/D in RTW conditions and RTD conditions, and the rates of growth are similar. The rate of growth in ETW conditions increases slower than the former two.
2020, 37(2): 276-283.
doi: 10.13801/j.cnki.fhclxb.20190514.002
Abstract:
In order to improve the bonding strength between polylactic acid (PLA) and aluminum alloy, PLA was reinforced by adding basalt fiber(BF). PLA and BF after drying were mixed by torque rheometer, and aluminum alloy surface was textured by fiber laser. The BF/PLA composites and the treated aluminum alloy were joined by a flat vulcanizing machine. The tensile strength of the BF/PLA-aluminum alloy composites was tested and the fracture surface was analyzed after failure. The results show that with the increase of BF mass fraction, the BF/PLA-aluminum alloy bonding strength shows a trend of strengthening first and then decreasing, and the increase of fiber mass fraction affects the crystallization and nucleation of the BF/PLA composite. Based on the experimental results, the finite element analysis model was established to simulate the tensile process of BF/PLA-aluminum alloy. The results show that the model can accurately restore the tensile process.
In order to improve the bonding strength between polylactic acid (PLA) and aluminum alloy, PLA was reinforced by adding basalt fiber(BF). PLA and BF after drying were mixed by torque rheometer, and aluminum alloy surface was textured by fiber laser. The BF/PLA composites and the treated aluminum alloy were joined by a flat vulcanizing machine. The tensile strength of the BF/PLA-aluminum alloy composites was tested and the fracture surface was analyzed after failure. The results show that with the increase of BF mass fraction, the BF/PLA-aluminum alloy bonding strength shows a trend of strengthening first and then decreasing, and the increase of fiber mass fraction affects the crystallization and nucleation of the BF/PLA composite. Based on the experimental results, the finite element analysis model was established to simulate the tensile process of BF/PLA-aluminum alloy. The results show that the model can accurately restore the tensile process.
2020, 37(2): 284-292.
doi: 10.13801/j.cnki.fhclxb.20190510.001
Abstract:
The impact dent relaxation characteristic has a crucial effect on probability of visual detection of low-velocity impact damage of aircraft composite structure. Laminate specimens were fabricated using T800 carbon fiber/M21 epoxy resin unidirectional prepreg tow auto-fiber-placing and autoclave curing process. The impact dent of about 1 mm was introduced on specimens, which were subsequently divided into 4 groups. The dent relaxation magnitudes in different periods were measured in room temperature ambient condition, elevated temperature wet condition respectively, cyclic loading condition and cyclic loading in elevated temperature wet condition, to study the effect of hygrothermal environment and cyclic loading on the impact dent relaxation. The results indicate:Hygrothermal environment obviously elevates the final relaxation magnitude of impact dent, yet the effect process is slow, therefore initial relaxation speed is nearly unaffected. Cyclic loading also elevates the final relaxation magnitude of impact dent, the effect of which is relatively insignificant. But it obviously elevates the initial relaxation speed. The effect on impact dent final relaxation magnitude of combination of hygrothermal environment and cyclic loading is larger than either of both, and the initial relaxation speed is almost the same as that in cyclic loading condition.
The impact dent relaxation characteristic has a crucial effect on probability of visual detection of low-velocity impact damage of aircraft composite structure. Laminate specimens were fabricated using T800 carbon fiber/M21 epoxy resin unidirectional prepreg tow auto-fiber-placing and autoclave curing process. The impact dent of about 1 mm was introduced on specimens, which were subsequently divided into 4 groups. The dent relaxation magnitudes in different periods were measured in room temperature ambient condition, elevated temperature wet condition respectively, cyclic loading condition and cyclic loading in elevated temperature wet condition, to study the effect of hygrothermal environment and cyclic loading on the impact dent relaxation. The results indicate:Hygrothermal environment obviously elevates the final relaxation magnitude of impact dent, yet the effect process is slow, therefore initial relaxation speed is nearly unaffected. Cyclic loading also elevates the final relaxation magnitude of impact dent, the effect of which is relatively insignificant. But it obviously elevates the initial relaxation speed. The effect on impact dent final relaxation magnitude of combination of hygrothermal environment and cyclic loading is larger than either of both, and the initial relaxation speed is almost the same as that in cyclic loading condition.
2020, 37(2): 293-301.
doi: 10.13801/j.cnki.fhclxb.20190430.002
Abstract:
The in-plane shear properties for the unbalanced 2.5D carbon fibre woven preforms (2.5D CFWPs) due to the changing of yarn linear density were investigated by the bias-tensile test. The test materials including 4 kinds of unbalanced 2.5D CFWPs and 1 kind of balanced 2.5D CFWPs. The typical bias-tensile modes and meso-structures were observed; The shear angles and bias-tensile load of balanced and unbalanced samples were compared and analyzed; Normalized method was used to analyze the influence of yarn linear density on the in-plane shear properties. The results show that the typical bias-tensile modes of the unbalanced 2.5D CFWPs are asymmetric S-shape or Z-shape. The bias-tensile properties of unbalanced 2.5D CFWP samples with yarn linear density of 792 tex×396 tex(the warp is 792 tex and the weft is 396 tex) are similar, the other 2 unbalanced samples are similar too; The bias-tensile load of the balanced samples is larger than the unbalanced, After locking angle, the bias-tensile load of the balanced samples is rising rapidly and the unbalanced is rising slowly; The normalized shear forces of the all 5 kinds of 2.5D CFWP samples are similar when the shear angle is less than 20.81°, and the 4 kinds of unbalanced samples are similar when the shear angle is between 20.81°-30.02°.
The in-plane shear properties for the unbalanced 2.5D carbon fibre woven preforms (2.5D CFWPs) due to the changing of yarn linear density were investigated by the bias-tensile test. The test materials including 4 kinds of unbalanced 2.5D CFWPs and 1 kind of balanced 2.5D CFWPs. The typical bias-tensile modes and meso-structures were observed; The shear angles and bias-tensile load of balanced and unbalanced samples were compared and analyzed; Normalized method was used to analyze the influence of yarn linear density on the in-plane shear properties. The results show that the typical bias-tensile modes of the unbalanced 2.5D CFWPs are asymmetric S-shape or Z-shape. The bias-tensile properties of unbalanced 2.5D CFWP samples with yarn linear density of 792 tex×396 tex(the warp is 792 tex and the weft is 396 tex) are similar, the other 2 unbalanced samples are similar too; The bias-tensile load of the balanced samples is larger than the unbalanced, After locking angle, the bias-tensile load of the balanced samples is rising rapidly and the unbalanced is rising slowly; The normalized shear forces of the all 5 kinds of 2.5D CFWP samples are similar when the shear angle is less than 20.81°, and the 4 kinds of unbalanced samples are similar when the shear angle is between 20.81°-30.02°.
2020, 37(2): 302-308.
doi: 10.13801/j.cnki.fhclxb.20190408.002
Abstract:
In order to establish the quantitative relationship between the damage index and delamination damage parameters for accurately quantitative monitoring delamintaion damage on stiffened composite panel, a quantitative monitoring method based on surrogate model was proposed. The initial samples acquired by impact experiment were used to construct polynomial surrogate model via the interpolation algorithm to represent the quantitative relationship between the delamination damage parameters and damage index. The quantitative monitoring process of delamination damage was that probability-based diagnostic imaging algorithm was used to localize the delamination damage and to acquire the relative distance and damage index, then the damage area was optimized by the polynomial surrogate model based on damage index and relative distance. The validity of the proposed quantitative monitoring method was assessed by quantitative monitoring damages at different locations with different areas on a stiffened composite panel. The experiment results show that the proposed method can quantity identify the damage of stiffened compo-site panel accurately. The error of damage location is below 6%, and the error of damage area is below 5%.
In order to establish the quantitative relationship between the damage index and delamination damage parameters for accurately quantitative monitoring delamintaion damage on stiffened composite panel, a quantitative monitoring method based on surrogate model was proposed. The initial samples acquired by impact experiment were used to construct polynomial surrogate model via the interpolation algorithm to represent the quantitative relationship between the delamination damage parameters and damage index. The quantitative monitoring process of delamination damage was that probability-based diagnostic imaging algorithm was used to localize the delamination damage and to acquire the relative distance and damage index, then the damage area was optimized by the polynomial surrogate model based on damage index and relative distance. The validity of the proposed quantitative monitoring method was assessed by quantitative monitoring damages at different locations with different areas on a stiffened composite panel. The experiment results show that the proposed method can quantity identify the damage of stiffened compo-site panel accurately. The error of damage location is below 6%, and the error of damage area is below 5%.
2020, 37(2): 309-317.
doi: 10.13801/j.cnki.fhclxb.20190310.001
Abstract:
The longitudinal tensile and compressive experiments on 3D 4-directional braided carbon fiber/epoxy resin composites with three different braiding angles were performed in thermal environments. The effects of temperature on the longitudinal tensile and compressive properties of 3D braided composites were discussed. Macro fracture morphology and SEM micrographs were examined to understand the damage and failure mechanism. The results show that the longitudinal tensile strength of 3D 4-directional braided carbon fiber/epoxy resin composites goes up slightly and the longitudinal compressive strength decreases obviously with the increase of testing temperature. The braiding angle has no apparent impact on the longitudinal tensile failure characteristics of composites. However, the effect of braiding angle on the longitudinal compressive failure characteristics of composites is obvious. As the temperature increases, the damage and failure patterns of 3D braided composites with three different braiding angles are obviously different than in room.
The longitudinal tensile and compressive experiments on 3D 4-directional braided carbon fiber/epoxy resin composites with three different braiding angles were performed in thermal environments. The effects of temperature on the longitudinal tensile and compressive properties of 3D braided composites were discussed. Macro fracture morphology and SEM micrographs were examined to understand the damage and failure mechanism. The results show that the longitudinal tensile strength of 3D 4-directional braided carbon fiber/epoxy resin composites goes up slightly and the longitudinal compressive strength decreases obviously with the increase of testing temperature. The braiding angle has no apparent impact on the longitudinal tensile failure characteristics of composites. However, the effect of braiding angle on the longitudinal compressive failure characteristics of composites is obvious. As the temperature increases, the damage and failure patterns of 3D braided composites with three different braiding angles are obviously different than in room.
2020, 37(2): 318-327.
doi: 10.13801/j.cnki.fhclxb.20190528.001
Abstract:
In order to alleviate the difficulty in thickness control and forming for paste adhesive layer in fabrication of carbon fiber reinforced polymer(CFRP) laminate-steel lap joints, a type of film adhesive was used to replace traditional paste adhesives. A total of 15 CFRP laminate-steel double lap joints connected with a film adhesive, with five kinds of bond lengths, were fabricated, and experimental studies were conducted focused on the failure modes, effective bond length, force transfer law, bond-slip constitutive and bearing capacity at room temperature. The results show that the bond strength of the film adhesive used is slightly higher than the interlaminar strength of the CFRP laminates (i.e. the bond strength between carbon fibers and resin matrix). The effective bond length of the film adhesive-connected CFRP laminate-steel joints at the room temperature is approximately 80 mm. At the beginning of loading, the maximum shear stress is located at the end of the joint steel plate. Its position moves towards the end of the joint CFRP laminate with the increase of load. At the end of loading, its position is located at 20 mm (when the bond length is less than 80 mm) or 50 mm (when the bond length is greater than 120 mm) from the end of the joint steel plate. The bond-slip relationship of film adhesive-connected CFRP laminate-steel lap joints can be simplified as a trapezoid model which is significantly different from the triangle model of paste adhesive-connected joints, suggesting that the ductility of the film adhesive-connected joints has been greatly improved. The representative values (quasi mean values) of peak shear stress, fracture energy and interfacial stiffness of the film adhesive-connected joints are 1.2-3.0 times, 1.6-5.7 times and 5.4-7.5 times, respectively, of those of joints with four typical paste adhesives. When the bond length is not less than the effective bond length, the representative value of tensile capacity of the film adhesive-connected joints are 1.25-2.39 times of the joints connected with paste adhesives. The variation coefficients of tensile strength and maximum displacement of the film adhesive-connected joins almost have no difference from the joints connected with paste adhesives.
In order to alleviate the difficulty in thickness control and forming for paste adhesive layer in fabrication of carbon fiber reinforced polymer(CFRP) laminate-steel lap joints, a type of film adhesive was used to replace traditional paste adhesives. A total of 15 CFRP laminate-steel double lap joints connected with a film adhesive, with five kinds of bond lengths, were fabricated, and experimental studies were conducted focused on the failure modes, effective bond length, force transfer law, bond-slip constitutive and bearing capacity at room temperature. The results show that the bond strength of the film adhesive used is slightly higher than the interlaminar strength of the CFRP laminates (i.e. the bond strength between carbon fibers and resin matrix). The effective bond length of the film adhesive-connected CFRP laminate-steel joints at the room temperature is approximately 80 mm. At the beginning of loading, the maximum shear stress is located at the end of the joint steel plate. Its position moves towards the end of the joint CFRP laminate with the increase of load. At the end of loading, its position is located at 20 mm (when the bond length is less than 80 mm) or 50 mm (when the bond length is greater than 120 mm) from the end of the joint steel plate. The bond-slip relationship of film adhesive-connected CFRP laminate-steel lap joints can be simplified as a trapezoid model which is significantly different from the triangle model of paste adhesive-connected joints, suggesting that the ductility of the film adhesive-connected joints has been greatly improved. The representative values (quasi mean values) of peak shear stress, fracture energy and interfacial stiffness of the film adhesive-connected joints are 1.2-3.0 times, 1.6-5.7 times and 5.4-7.5 times, respectively, of those of joints with four typical paste adhesives. When the bond length is not less than the effective bond length, the representative value of tensile capacity of the film adhesive-connected joints are 1.25-2.39 times of the joints connected with paste adhesives. The variation coefficients of tensile strength and maximum displacement of the film adhesive-connected joins almost have no difference from the joints connected with paste adhesives.
2020, 37(2): 328-335.
doi: 10.13801/j.cnki.fhclxb.20190701.002
Abstract:
In order to study the damage mechanics and the effects of some factors on the dynamic response of the composite honeycomb sandwich panels under the bird impact, the impact of gelatin bird on the composite honeycomb sandwich panels experiment was conducted. CT scanning technology was used to detect the inside of the composite honeycomb sandwich panel. Delamination, matrix cracking, fiber fracture, dent and buckling occur in panels; crushing and debonding with panel occur in the honeycomb core; The dynamic deformation and displacement-time data of rear panel of composite honeycomb sandwich panels were analyzed. The global bending deformation and local deformation appear in the sandwich panels during the impact; The comparative analysis was carried out, the damage level of the composite honeycomb sandwich panels increases with the increase of the impact speed; the composite honeycomb sandwich panel with a thickness of 10 mm is more severe than the composite honeycomb sandwich panel with a thickness of 5 mm in the damage level; the spherical bird with higher initial kinetic energy causes more damage to the composite honeycomb sandwich panel than the cylindrical bird.
In order to study the damage mechanics and the effects of some factors on the dynamic response of the composite honeycomb sandwich panels under the bird impact, the impact of gelatin bird on the composite honeycomb sandwich panels experiment was conducted. CT scanning technology was used to detect the inside of the composite honeycomb sandwich panel. Delamination, matrix cracking, fiber fracture, dent and buckling occur in panels; crushing and debonding with panel occur in the honeycomb core; The dynamic deformation and displacement-time data of rear panel of composite honeycomb sandwich panels were analyzed. The global bending deformation and local deformation appear in the sandwich panels during the impact; The comparative analysis was carried out, the damage level of the composite honeycomb sandwich panels increases with the increase of the impact speed; the composite honeycomb sandwich panel with a thickness of 10 mm is more severe than the composite honeycomb sandwich panel with a thickness of 5 mm in the damage level; the spherical bird with higher initial kinetic energy causes more damage to the composite honeycomb sandwich panel than the cylindrical bird.
2020, 37(2): 336-344.
doi: 10.13801/j.cnki.fhclxb.20190417.004
Abstract:
The multifunctional composites embedded with multi-walled carbon nanotube (MWCNT) interfacial sensor were manufactured, and its application in the in-situ monitoring of a filament wound pressure vessel was carried out. The reliability of the MWCNT interfacial sensor serviced in the complex environment was firstly considered. The effect of MWCNT on the interfacial shear strength (IFSS) was analyzed, and the water absorption characteristics of the composites with interfacial sensor in water were obtained. The in-situ monitoring and healing of interfacial damage were performed based on the embedded interfacial sensor, and the feasibility of this method was discussed. The MWCNT interfacial sensor was finally embedded into a filament wound pressure vessel, and the in-situ monitoring experiments of the vessel under hydraulic fatigue cycling and pressurization load were performed. The results show that IFSS could be enhanced by embedding MWCNT interfacial sensor, and its decreasing ratio shows a decreasing tendency in the special conditions. The interfacial damage in the thermoplastic composites could be successfully monitored and healed by the MWCNT interfacial sensor. The interfacial damage in the filament wound pressure vessel could also be in-situ monitored by the MWCNT interfacial sensor.
The multifunctional composites embedded with multi-walled carbon nanotube (MWCNT) interfacial sensor were manufactured, and its application in the in-situ monitoring of a filament wound pressure vessel was carried out. The reliability of the MWCNT interfacial sensor serviced in the complex environment was firstly considered. The effect of MWCNT on the interfacial shear strength (IFSS) was analyzed, and the water absorption characteristics of the composites with interfacial sensor in water were obtained. The in-situ monitoring and healing of interfacial damage were performed based on the embedded interfacial sensor, and the feasibility of this method was discussed. The MWCNT interfacial sensor was finally embedded into a filament wound pressure vessel, and the in-situ monitoring experiments of the vessel under hydraulic fatigue cycling and pressurization load were performed. The results show that IFSS could be enhanced by embedding MWCNT interfacial sensor, and its decreasing ratio shows a decreasing tendency in the special conditions. The interfacial damage in the thermoplastic composites could be successfully monitored and healed by the MWCNT interfacial sensor. The interfacial damage in the filament wound pressure vessel could also be in-situ monitored by the MWCNT interfacial sensor.
2020, 37(2): 345-355.
doi: 10.13801/j.cnki.fhclxb.20190506.001
Abstract:
To improve the vehicle lightweight and crashworthiness, a design strategy for the characteristics of carbon fiber reinforced polymer composite anti-collision beam structure was proposed based on grey relational analysis with the entropy weight method. A numerical simplified model considering the actual working condition of the whole vehicle was established. The mechanical properties of the material were determined by the mechanical properties test of carbon fiber reinforced plastics, which provides accurate material property for the carbon fiber bumper anti-collision beam model under collision conditions. The Hammersley experimental design method can generate 60 sample points to establish the relationship between design variables and responses based on the frontal collision simulation model. The entropy weight method was used to determine the weight of each response index, and the crashworthiness and lightweight of the composite anti-collision beam were optimized by the grey relational analysis method. The optimal size parameter combination of the anti-collision beam structure was obtained and the optimization scheme was determined. The results show that the optimal model peak energy absorption is increased by 11.4%, the peak force is reduced by 48%, and the mass is reduced by 56.5% compared with the initial model. The method achieves lightweight optimization design for the vehide under the premise that the safety index is satisfied.
To improve the vehicle lightweight and crashworthiness, a design strategy for the characteristics of carbon fiber reinforced polymer composite anti-collision beam structure was proposed based on grey relational analysis with the entropy weight method. A numerical simplified model considering the actual working condition of the whole vehicle was established. The mechanical properties of the material were determined by the mechanical properties test of carbon fiber reinforced plastics, which provides accurate material property for the carbon fiber bumper anti-collision beam model under collision conditions. The Hammersley experimental design method can generate 60 sample points to establish the relationship between design variables and responses based on the frontal collision simulation model. The entropy weight method was used to determine the weight of each response index, and the crashworthiness and lightweight of the composite anti-collision beam were optimized by the grey relational analysis method. The optimal size parameter combination of the anti-collision beam structure was obtained and the optimization scheme was determined. The results show that the optimal model peak energy absorption is increased by 11.4%, the peak force is reduced by 48%, and the mass is reduced by 56.5% compared with the initial model. The method achieves lightweight optimization design for the vehide under the premise that the safety index is satisfied.
2020, 37(2): 356-365.
doi: 10.13801/j.cnki.fhclxb.20190515.001
Abstract:
In order to deeply analyze the damage mechanism of carbon fiber reinforced polymer(CFRP) composite with fastener and the influence of specimen size on the damage area of CFRP under lightning environment, the lightning damage experiment and simulation research were carried out on two different sizes of CFRP with fastener. According to the thermo-electric coupling theory, the thermo-electric coupling model of mechanical fastened CFRP was established by ABAQUS, and the temperature field distribution of CFRP under the action of single lightning current A component was obtained. The damage characteristics of CFRP under lightning damage experiment were evaluated using the ultrasonic C-scan. Under this lightning strike condition, the experimental and simulation results show that the lightning current is spreading throughout the thickness of the CFRP specimen through the fastener. The damage area of the CFRP specimen is small when the amplitude of the lightning current is not too large, but the damage area increases sharply and specimen delaminate throughout the thickness with the increase of the current amplitude. The damage stratification, damage morphology and area of CFRP with fastener of different sizes are similar at the similar current, the specimen size variation has little influence on the damage characteristics. The experimental and simulation studies provide a simulated and experimental data support for the structural design of CFRP.
In order to deeply analyze the damage mechanism of carbon fiber reinforced polymer(CFRP) composite with fastener and the influence of specimen size on the damage area of CFRP under lightning environment, the lightning damage experiment and simulation research were carried out on two different sizes of CFRP with fastener. According to the thermo-electric coupling theory, the thermo-electric coupling model of mechanical fastened CFRP was established by ABAQUS, and the temperature field distribution of CFRP under the action of single lightning current A component was obtained. The damage characteristics of CFRP under lightning damage experiment were evaluated using the ultrasonic C-scan. Under this lightning strike condition, the experimental and simulation results show that the lightning current is spreading throughout the thickness of the CFRP specimen through the fastener. The damage area of the CFRP specimen is small when the amplitude of the lightning current is not too large, but the damage area increases sharply and specimen delaminate throughout the thickness with the increase of the current amplitude. The damage stratification, damage morphology and area of CFRP with fastener of different sizes are similar at the similar current, the specimen size variation has little influence on the damage characteristics. The experimental and simulation studies provide a simulated and experimental data support for the structural design of CFRP.
2020, 37(2): 366-375.
doi: 10.13801/j.cnki.fhclxb.20190529.002
Abstract:
A piezoelectric-mechanical coupled finite element model of composite laminated shells with piezoelectric layers was presented. The Reddy's layerwise laminate theory was used to derive the according expressions of strains and electric field, the Euler-Lagrange equations were obtained by employing Hamilton's principle and variational method, and then a finite element model and the according piezoelectric-mechanical coupled stiffness were formulated based on the developed layerwise mechanics. Numerical examples were implemented to evaluate the efficiency and accuracy of the present method by comparing with the results obtained with classical laminated plate theory. The effects of radius to thickness ratio of a simply-supported laminated piezoelectric composite shell for static response were also investigated in the end.
A piezoelectric-mechanical coupled finite element model of composite laminated shells with piezoelectric layers was presented. The Reddy's layerwise laminate theory was used to derive the according expressions of strains and electric field, the Euler-Lagrange equations were obtained by employing Hamilton's principle and variational method, and then a finite element model and the according piezoelectric-mechanical coupled stiffness were formulated based on the developed layerwise mechanics. Numerical examples were implemented to evaluate the efficiency and accuracy of the present method by comparing with the results obtained with classical laminated plate theory. The effects of radius to thickness ratio of a simply-supported laminated piezoelectric composite shell for static response were also investigated in the end.
2020, 37(2): 376-381.
doi: 10.13801/j.cnki.fhclxb.20190328.001
Abstract:
Panel separating from honeycomb core caused by the adhesive property decreasing is the main reason which make the mechanical properties of honeycomb sandwich panel degenerate at high temperatures. Equivalent debonding coefficient and temperature retention coefficients of elastic modulus of panel and honeycomb core were defined as damage variables to reflect the extent of the damage for the bending stiffness of honeycomb sandwich panel at high temperatures. A mechanics model for bending stiffness of honeycomb sandwich structure decreasing with temperature rising was created. It shows that the physical model can reflect the principle of the bending stiffness degenerating with temperature rising perfectly. The difference between the calculated and the experimental result is less than 15%, which achieves the goal that forecasting the bending stiffness of honeycomb sandwich panel at high temperatures correctly. This research can be used to estimate the bending stiffness of soft honeycomb sandwich structure at high temperatures.
Panel separating from honeycomb core caused by the adhesive property decreasing is the main reason which make the mechanical properties of honeycomb sandwich panel degenerate at high temperatures. Equivalent debonding coefficient and temperature retention coefficients of elastic modulus of panel and honeycomb core were defined as damage variables to reflect the extent of the damage for the bending stiffness of honeycomb sandwich panel at high temperatures. A mechanics model for bending stiffness of honeycomb sandwich structure decreasing with temperature rising was created. It shows that the physical model can reflect the principle of the bending stiffness degenerating with temperature rising perfectly. The difference between the calculated and the experimental result is less than 15%, which achieves the goal that forecasting the bending stiffness of honeycomb sandwich panel at high temperatures correctly. This research can be used to estimate the bending stiffness of soft honeycomb sandwich structure at high temperatures.
2020, 37(2): 382-389.
doi: 10.13801/j.cnki.fhclxb.20190611.001
Abstract:
The theoretical solving techniques of vibration responses of fiber reinforced resin composite thin cylindrical shell in thermal environment were studied. Considering the influences of base excitation load and thermal environment, a theoretical model of the shell with such kind of materials was established, where the constitutive relations, physical equations and energy equations of the materials and structures were determined based on the plate and shell theory, complex elastic modulus approach, etc. The vibration mode function was represented by the bidirectional beam function method, so that the frequency domain vibration response can be successfully solved by the Ritz method and the mode superposition approach with the proportional damping being introduced. A TC300 fiber/epoxy resin composite cylindrical shell was taken as a study object. The first 3 frequency response curves of the shell structure were measured. It has been found that compared with the first 3 resonant responses measured, the error of resonant responses obtained by theoretical calculation is less than 14.8%. Thus, the correctness and effectiveness of the analytical method proposed have been verified.
The theoretical solving techniques of vibration responses of fiber reinforced resin composite thin cylindrical shell in thermal environment were studied. Considering the influences of base excitation load and thermal environment, a theoretical model of the shell with such kind of materials was established, where the constitutive relations, physical equations and energy equations of the materials and structures were determined based on the plate and shell theory, complex elastic modulus approach, etc. The vibration mode function was represented by the bidirectional beam function method, so that the frequency domain vibration response can be successfully solved by the Ritz method and the mode superposition approach with the proportional damping being introduced. A TC300 fiber/epoxy resin composite cylindrical shell was taken as a study object. The first 3 frequency response curves of the shell structure were measured. It has been found that compared with the first 3 resonant responses measured, the error of resonant responses obtained by theoretical calculation is less than 14.8%. Thus, the correctness and effectiveness of the analytical method proposed have been verified.
2020, 37(2): 390-399.
doi: 10.13801/j.cnki.fhclxb.20190506.002
Abstract:
The durability of basalt fiber reinforced polymer (BFRP) and epoxy resin in ultraviolet radiation environment was studied by accelerated aging test using ultraviolet radiation aging chamber to simulate ultraviolet radiation in atmospheric environment. Based on the changes of tensile strength, modulus of elasticity and elongation at break of BFRP and epoxy resin after ultraviolet aging, combined with the method of deep belief network(DBN), the changing trend of tensile strength and modulus of elasticity of BFRP and epoxy resin was predicted, and the modulus of elasticity of non-destructive samples in the same batch was proposed as the evaluation index of durability of BFRP. The results show that the tensile strength and elongation at break of BFRP and epoxy resin increase first and then decrease with aging time, but the modulus of elasticity tends to decrease gently. The relative error between the predicted value and experimental value obtained by DBN is less than 10%. The validity of predicting durability of BFRP and epoxy resin by DBN is non-destructive. It is more scientific to evaluate the durability of BFRP by the elastic modulus of sexual specimens.
The durability of basalt fiber reinforced polymer (BFRP) and epoxy resin in ultraviolet radiation environment was studied by accelerated aging test using ultraviolet radiation aging chamber to simulate ultraviolet radiation in atmospheric environment. Based on the changes of tensile strength, modulus of elasticity and elongation at break of BFRP and epoxy resin after ultraviolet aging, combined with the method of deep belief network(DBN), the changing trend of tensile strength and modulus of elasticity of BFRP and epoxy resin was predicted, and the modulus of elasticity of non-destructive samples in the same batch was proposed as the evaluation index of durability of BFRP. The results show that the tensile strength and elongation at break of BFRP and epoxy resin increase first and then decrease with aging time, but the modulus of elasticity tends to decrease gently. The relative error between the predicted value and experimental value obtained by DBN is less than 10%. The validity of predicting durability of BFRP and epoxy resin by DBN is non-destructive. It is more scientific to evaluate the durability of BFRP by the elastic modulus of sexual specimens.
2020, 37(2): 400-407.
doi: 10.13801/j.cnki.fhclxb.20190524.001
Abstract:
By using a kind of composite nanofibers with core-shell structure to reinforce aluminum alloy matrix composites, it can improve the tensile strength while increasing plasticity. Al2O3@Y3Al5O12 short nanofibers reinforced 2024 aluminum alloy composites were prepared by vacuum hot-pressing sintering technique. The effects of Al2O3@Y3Al5O12 nanofibers content on the relative density, hardness, tensile strength and elongation of composites were studied, and the effect of the core-shell structure on the toughening mechanism of the composites explored. The results show that the Al2O3@Y3Al5O12 short nanofibers have good dispersion, and the fibers are uniformly adsorbed on the surface of aluminum alloy particles without stratification and agglomeration was method of ultrasonic dispersion and mechanical agitation. After hot-pressing sintering, the Al2O3@Y3Al5O12 short nanofibers are uniformly dispersed in the aluminum alloy matrix with a form of short fibers, and a small content of Al2O3@Y3Al5O12 short nanofibers plays the role of bridging and hole filling, which increases the relative density and hardness of the composites. There are the maximum tensile strength and elongation of the composites at the nanofiber mass fraction of 1wt%, which increase from 249.3 MPa (matrix) to 299.1 MPa, 2.9% (matrix) to 4.3%, respectively. The addition of Y3Al5O12-Al2O3 short nanofibers can refine the composites grain, hinder crack propagation, and the plastic deformation of Y3Al5O12-Al2O3 core-shell structure plays a strengthening and toughening effect in the process of pulling out/breaking.
By using a kind of composite nanofibers with core-shell structure to reinforce aluminum alloy matrix composites, it can improve the tensile strength while increasing plasticity. Al2O3@Y3Al5O12 short nanofibers reinforced 2024 aluminum alloy composites were prepared by vacuum hot-pressing sintering technique. The effects of Al2O3@Y3Al5O12 nanofibers content on the relative density, hardness, tensile strength and elongation of composites were studied, and the effect of the core-shell structure on the toughening mechanism of the composites explored. The results show that the Al2O3@Y3Al5O12 short nanofibers have good dispersion, and the fibers are uniformly adsorbed on the surface of aluminum alloy particles without stratification and agglomeration was method of ultrasonic dispersion and mechanical agitation. After hot-pressing sintering, the Al2O3@Y3Al5O12 short nanofibers are uniformly dispersed in the aluminum alloy matrix with a form of short fibers, and a small content of Al2O3@Y3Al5O12 short nanofibers plays the role of bridging and hole filling, which increases the relative density and hardness of the composites. There are the maximum tensile strength and elongation of the composites at the nanofiber mass fraction of 1wt%, which increase from 249.3 MPa (matrix) to 299.1 MPa, 2.9% (matrix) to 4.3%, respectively. The addition of Y3Al5O12-Al2O3 short nanofibers can refine the composites grain, hinder crack propagation, and the plastic deformation of Y3Al5O12-Al2O3 core-shell structure plays a strengthening and toughening effect in the process of pulling out/breaking.
2020, 37(2): 408-414.
doi: 10.13801/j.cnki.fhclxb.20190426.001
Abstract:
The stress intensity factor is used in fracture mechanics to predict the stress state near the tip of a crack caused by a remote load or residual stresses. In this paper, the law between WCP shape and its tip stress was established in a finite plate under uniaxial stress based on stress intensity factor, the thermal stress of WCP/Fe compo-sites with different particle shapes were simulated through finite element analysis software, the effect of WCP shape on the thermal fatigue crack propagation behavior of WCP composites was studied. The results show that the WCP shape significantly affects the stress intensity factor and the thermal fatigue crack propagation behavior of WCP/Fe composites. The ultimate compressive strength of WCP/Fe composites with spherical particles and irregular ones are 460 MPa and 370 MPa, respectively. The WCP/Fe composites with irregular particles are prone to break due to stress concentration resulting in generating brittle cracking. The thermal shock test was used to verify the simulation results, finding that the experimental results are similar to the simulation results, which confirms the correctness of finite element simulation, and provides a scientific and theoretical basis for the study of thermal fatigue crack propagation behavior of WCP/Fe composites.
The stress intensity factor is used in fracture mechanics to predict the stress state near the tip of a crack caused by a remote load or residual stresses. In this paper, the law between WCP shape and its tip stress was established in a finite plate under uniaxial stress based on stress intensity factor, the thermal stress of WCP/Fe compo-sites with different particle shapes were simulated through finite element analysis software, the effect of WCP shape on the thermal fatigue crack propagation behavior of WCP composites was studied. The results show that the WCP shape significantly affects the stress intensity factor and the thermal fatigue crack propagation behavior of WCP/Fe composites. The ultimate compressive strength of WCP/Fe composites with spherical particles and irregular ones are 460 MPa and 370 MPa, respectively. The WCP/Fe composites with irregular particles are prone to break due to stress concentration resulting in generating brittle cracking. The thermal shock test was used to verify the simulation results, finding that the experimental results are similar to the simulation results, which confirms the correctness of finite element simulation, and provides a scientific and theoretical basis for the study of thermal fatigue crack propagation behavior of WCP/Fe composites.
2020, 37(2): 415-421.
doi: 10.13801/j.cnki.fhclxb.20190510.003
Abstract:
C-TiO2 composites were successfully prepared via sol-gel method with assistance of microcrystalline cellulose(CMC). The structure, components and morphology of C-TiO2 composites have been fully studied. The results of XRD show that:C-TiO2 composite has the structure of anatase with high crystallinity; the analyses of SEM, TEM and XPS give the evidence that cellulose has dual effects on the preparation of the C-TiO2 composite:it is the precursor of carbon, and it also works as dispersant which makes TiO2 well dispersive. The adsorption experiments of Cd2+ has been carried out to evaluate the adsorption property by the C-TiO2 composite. Compared with the TiO2 prepared without cellulose, C-TiO2 composite has high adsorption. The adsorption amount of Cd2+ reaches 37.15 mgg-1, which is 214.5% as higher as that without cellulose. At the same time, C-TiO2 composite has excellent adsorption efficiency, which makes C-TiO2 a good candidate for water treatment.
C-TiO2 composites were successfully prepared via sol-gel method with assistance of microcrystalline cellulose(CMC). The structure, components and morphology of C-TiO2 composites have been fully studied. The results of XRD show that:C-TiO2 composite has the structure of anatase with high crystallinity; the analyses of SEM, TEM and XPS give the evidence that cellulose has dual effects on the preparation of the C-TiO2 composite:it is the precursor of carbon, and it also works as dispersant which makes TiO2 well dispersive. The adsorption experiments of Cd2+ has been carried out to evaluate the adsorption property by the C-TiO2 composite. Compared with the TiO2 prepared without cellulose, C-TiO2 composite has high adsorption. The adsorption amount of Cd2+ reaches 37.15 mgg-1, which is 214.5% as higher as that without cellulose. At the same time, C-TiO2 composite has excellent adsorption efficiency, which makes C-TiO2 a good candidate for water treatment.
2020, 37(2): 422-431.
doi: 10.13801/j.cnki.fhclxb.20190508.001
Abstract:
The NiS2/reduced graphene oxide(3D rGO) composite with the 3D porous structure was successfully synthesized via a facile one-step solvothermal method using a suitable soft template. The surface morphology, valence of the elements and electrochemical performance of the samples were characterized by FESEM, TEM, XPS and the electrochemical workstation. The results show that the NiS2/3D rGO composite has a three-dimensional stacked pore structure of graphene and high specific surface areas. The specific surface area is 57.51 m2g-1. Electrochemical measurements show that the NiS2/3D rGO microsphere electrode reveals amazing pseudocapacitive properties with high specific capacitance (1 116.7 Fg-1 at current density of 1 Ag-1) and a favorable rate capability (74.5% from 1 to 5 Ag-1), Moreover, the specific capacitance remains 91.2% of its initial value after 1 000 cycles at current density of 4 Ag-1. Therefore, NiS2/3D rGO composite can be used as a promising electrode material for the supercapacitor.
The NiS2/reduced graphene oxide(3D rGO) composite with the 3D porous structure was successfully synthesized via a facile one-step solvothermal method using a suitable soft template. The surface morphology, valence of the elements and electrochemical performance of the samples were characterized by FESEM, TEM, XPS and the electrochemical workstation. The results show that the NiS2/3D rGO composite has a three-dimensional stacked pore structure of graphene and high specific surface areas. The specific surface area is 57.51 m2g-1. Electrochemical measurements show that the NiS2/3D rGO microsphere electrode reveals amazing pseudocapacitive properties with high specific capacitance (1 116.7 Fg-1 at current density of 1 Ag-1) and a favorable rate capability (74.5% from 1 to 5 Ag-1), Moreover, the specific capacitance remains 91.2% of its initial value after 1 000 cycles at current density of 4 Ag-1. Therefore, NiS2/3D rGO composite can be used as a promising electrode material for the supercapacitor.
2020, 37(2): 432-441.
doi: 10.13801/j.cnki.fhclxb.20190516.001
Abstract:
In order to study the effect of suture on the tensile properties of thermal protection structures, a suture-stitched reinforced sandwich structure (ceramic-aerogel-ceramic) model was proposed. With the help of finite element software programming language modeling, the internal stress-strain field of the stitched reinforced sandwich structure was determined by multi-step stepwise and accurate analysis. Firstly, the finite element analysis of the stent and the experimental piece without suture was carried out; then the detailed structure such as suture was considered; finally, the substructure was taken for detailed analysis. The stress variation trend of the sandwich structure finite element model was compared with the test results of the test piece. The validity of the finite element model was verified and the variation law of the finite element solution was given. The stress-strain curves obtained by the stitching reinforced sandwich structure and the unstitched sandwich structure were compared. The results show that when the structural bottom plate is uniaxially stretched and the suture is prestressed, the stress peak of the suture reinforced sandwich structure along the length direction (x direction) can be effectively reduced (the maximum stress on path 1 is reduced by 4.6%); the stress along the z direction (path 3 is reduced by 30% on average) can be drastically reduced.
In order to study the effect of suture on the tensile properties of thermal protection structures, a suture-stitched reinforced sandwich structure (ceramic-aerogel-ceramic) model was proposed. With the help of finite element software programming language modeling, the internal stress-strain field of the stitched reinforced sandwich structure was determined by multi-step stepwise and accurate analysis. Firstly, the finite element analysis of the stent and the experimental piece without suture was carried out; then the detailed structure such as suture was considered; finally, the substructure was taken for detailed analysis. The stress variation trend of the sandwich structure finite element model was compared with the test results of the test piece. The validity of the finite element model was verified and the variation law of the finite element solution was given. The stress-strain curves obtained by the stitching reinforced sandwich structure and the unstitched sandwich structure were compared. The results show that when the structural bottom plate is uniaxially stretched and the suture is prestressed, the stress peak of the suture reinforced sandwich structure along the length direction (x direction) can be effectively reduced (the maximum stress on path 1 is reduced by 4.6%); the stress along the z direction (path 3 is reduced by 30% on average) can be drastically reduced.
2020, 37(2): 442-450.
doi: 10.13801/j.cnki.fhclxb.20190527.001
Abstract:
In order to investigate the response characteristics of composites under strong electromagnetic pulse, Ag nanowires (AgNWs) with high aspect ratio were synthesized using polyol method. AgNWs/polyvinyl alcohol (PVA) composite samples with different volume fractions were prepared using PVA as the matrix. The nonlinear conductive behaviors and electromagnetic pulse response characteristics of AgNWs/PVA composites were tested using a power device analyzer and a dynamic response testing system, respectively. The results show that AgNWs/PVA composites within a certain concentration range have excellent nonlinear conductivity characteristics. At the threshold voltage, the conductivity of AgNWs/PVA composites increases rapidly, and the current has a large jump of about 4 orders of magnitude. The nonlinear coefficient α of AgNWs/PVA composite with 1.05vol% volume fraction of AgNWs can be up to 1 959.89. In the vicinity of the square pulse threshold voltage of AgNWs/PVA compo-sites, the voltage amplitude of the output waveform attenuates effectively, which reveals that the conductivity of the AgNWs/PVA composites increases sharply under strong electromagnetic pulse. The AgNWs/PVA composites have the low-pass characteristics of electromagnetic energy, and have a broad application prospect in the field of strong electromagnetic pulse protection of electronic equipment with the function of sending and receiving information.
In order to investigate the response characteristics of composites under strong electromagnetic pulse, Ag nanowires (AgNWs) with high aspect ratio were synthesized using polyol method. AgNWs/polyvinyl alcohol (PVA) composite samples with different volume fractions were prepared using PVA as the matrix. The nonlinear conductive behaviors and electromagnetic pulse response characteristics of AgNWs/PVA composites were tested using a power device analyzer and a dynamic response testing system, respectively. The results show that AgNWs/PVA composites within a certain concentration range have excellent nonlinear conductivity characteristics. At the threshold voltage, the conductivity of AgNWs/PVA composites increases rapidly, and the current has a large jump of about 4 orders of magnitude. The nonlinear coefficient α of AgNWs/PVA composite with 1.05vol% volume fraction of AgNWs can be up to 1 959.89. In the vicinity of the square pulse threshold voltage of AgNWs/PVA compo-sites, the voltage amplitude of the output waveform attenuates effectively, which reveals that the conductivity of the AgNWs/PVA composites increases sharply under strong electromagnetic pulse. The AgNWs/PVA composites have the low-pass characteristics of electromagnetic energy, and have a broad application prospect in the field of strong electromagnetic pulse protection of electronic equipment with the function of sending and receiving information.
2020, 37(2): 451-460.
doi: 10.13801/j.cnki.fhclxb.20190717.002
Abstract:
Polyvinyl alcohol fiber reinforced cement (PVA/C) composites have superior tensile strain hardening characteristics, which can significantly improve the deformation capacity of the structure. Based on the PVA fiber volume fraction and the reinforcement ratio, the four-point bending experiment of six steel reinforced PVA/RC beams and two ordinary concrete (C) beams was carried out, and the ductility of the steel reinforced PVA/RC beams was analyzed. The experimental research shows that the area surrounded by the load-deflection curve of the steel reinforced PVA/C beams is 1.64-3.71 times of the RC beam, which proves that the steel reinforced PVA/RC beams have better holding deformation ability. When the PVA fiber volume fraction is constant, the curvature ductility coefficient of the test beam decreases with the increase of the reinforcement ratios. In the case of a certain reinforcement ratio, the curvature ductility coefficients of the steel reinforced PVA/C beams are 1.56-2.02 times that of the C beam, which proves that the incorporation of PVA fiber significantly improves the ductility of the test beam. The calculation formula of the curvature ductility coefficient of the steel reinforced PVA/C beams was established, and the influence of the PVA fiber volume fraction on the ductility coefficient and the height coefficient of pressurized zone was analyzed. The test results are in good agreement with the calculated results.
Polyvinyl alcohol fiber reinforced cement (PVA/C) composites have superior tensile strain hardening characteristics, which can significantly improve the deformation capacity of the structure. Based on the PVA fiber volume fraction and the reinforcement ratio, the four-point bending experiment of six steel reinforced PVA/RC beams and two ordinary concrete (C) beams was carried out, and the ductility of the steel reinforced PVA/RC beams was analyzed. The experimental research shows that the area surrounded by the load-deflection curve of the steel reinforced PVA/C beams is 1.64-3.71 times of the RC beam, which proves that the steel reinforced PVA/RC beams have better holding deformation ability. When the PVA fiber volume fraction is constant, the curvature ductility coefficient of the test beam decreases with the increase of the reinforcement ratios. In the case of a certain reinforcement ratio, the curvature ductility coefficients of the steel reinforced PVA/C beams are 1.56-2.02 times that of the C beam, which proves that the incorporation of PVA fiber significantly improves the ductility of the test beam. The calculation formula of the curvature ductility coefficient of the steel reinforced PVA/C beams was established, and the influence of the PVA fiber volume fraction on the ductility coefficient and the height coefficient of pressurized zone was analyzed. The test results are in good agreement with the calculated results.
2020, 37(2): 461-471.
doi: 10.13801/j.cnki.fhclxb.20190528.002
Abstract:
In order to study the shear property and shear toughness evaluation method of highly ductile concrete(HDC), 5 sets of HDC specimens, 1 set of matrix specimens (without fiber) and 1 set of concrete specimens were designed for comparison. Through double shear experiment, fiber volume fraction and HDC compressive strength were set into parameters to analysis the modes of shear failure, shear strength of HDC specimens and deformation at peak load. Based on the results of experiment, shear toughness evaluation method of HDC double shear experiment was built. The research shows that:with the bridging action of fiber in HDC and during fiber pull-out, it has absorbed considerable energy. The shear failure mode of HDC specimens is ductile failure; Compared with concrete and matrix specimens, the shear strength and the deformation at peak load of HDC specimens are substantially improved, and its range of improvement increases with the increasing number of fiber volume fraction; With the increasing of HDC compressive strength, the shear strength of the HDC specimens increases gradually, and the shear deformation at peak load decreases gradually; Using initial energy density and residual shear toughness ratio to evaluate the shear toughness of HDC materials, the shear toughness of HDC specimen has a significantly higher level than concrete and matrix specimens.
In order to study the shear property and shear toughness evaluation method of highly ductile concrete(HDC), 5 sets of HDC specimens, 1 set of matrix specimens (without fiber) and 1 set of concrete specimens were designed for comparison. Through double shear experiment, fiber volume fraction and HDC compressive strength were set into parameters to analysis the modes of shear failure, shear strength of HDC specimens and deformation at peak load. Based on the results of experiment, shear toughness evaluation method of HDC double shear experiment was built. The research shows that:with the bridging action of fiber in HDC and during fiber pull-out, it has absorbed considerable energy. The shear failure mode of HDC specimens is ductile failure; Compared with concrete and matrix specimens, the shear strength and the deformation at peak load of HDC specimens are substantially improved, and its range of improvement increases with the increasing number of fiber volume fraction; With the increasing of HDC compressive strength, the shear strength of the HDC specimens increases gradually, and the shear deformation at peak load decreases gradually; Using initial energy density and residual shear toughness ratio to evaluate the shear toughness of HDC materials, the shear toughness of HDC specimen has a significantly higher level than concrete and matrix specimens.
2020, 37(2): 472-481.
doi: 10.13801/j.cnki.fhclxb.20190428.001
Abstract:
The infrared thermal imaging(IRT) detection technology is often utilized for the debonding detection of concrete reinforced by fiber reinforced plastics (FRP) sheets. However, the traditional heat source excitation IRT method is affected by factors such as short heating distance, low thermal sensitivity and high power consumption. In order to solve these problems, the debonding detection of FRP-reinforced concrete structures based on optical excitation line laser heat source IRT method was proposed. The IRT method based on optical excitation line laser heat source was proposed to detect the debonding of FRP reinforced concrete. The surface local heat distribution anomalies caused by debonding in the structure could be measured by an infrared camera. Based on the numerical and experimental results, it is proved that the method has the advantages of debonding detection in FRP-reinforced concrete structure. This method has advantages:the feasibility of using laser scanning thermal imaging technology to detect the debonding damage in FRP reinforced concrete structure; FRP reinforcement long-distance, high thermal sensitivity and low power consumption damage detection of FRP reinforced concrete structures.
The infrared thermal imaging(IRT) detection technology is often utilized for the debonding detection of concrete reinforced by fiber reinforced plastics (FRP) sheets. However, the traditional heat source excitation IRT method is affected by factors such as short heating distance, low thermal sensitivity and high power consumption. In order to solve these problems, the debonding detection of FRP-reinforced concrete structures based on optical excitation line laser heat source IRT method was proposed. The IRT method based on optical excitation line laser heat source was proposed to detect the debonding of FRP reinforced concrete. The surface local heat distribution anomalies caused by debonding in the structure could be measured by an infrared camera. Based on the numerical and experimental results, it is proved that the method has the advantages of debonding detection in FRP-reinforced concrete structure. This method has advantages:the feasibility of using laser scanning thermal imaging technology to detect the debonding damage in FRP reinforced concrete structure; FRP reinforcement long-distance, high thermal sensitivity and low power consumption damage detection of FRP reinforced concrete structures.
2020, 37(2): 482-491.
doi: 10.13801/j.cnki.fhclxb.20190701.003
Abstract:
According to the repeatability of the composite cell structure, a dynamic modeling method for stitched sandwich panel based on the repetitive substructure was proposed. The primary substructure and the residual structure were constructed by using the precise finite element model of the composite unit cell. The repetitive substructure was obtained by mapping the spatial position relation. All the substructures were assembled on the residual structure to realize the dynamic modeling and analysis of the repetitive substructure of the composite. Taking the stitched sandwich panel as an example, the repetitive substructure modeling and dynamic characteristic analysis were carried out, and compared with the precise solid finite element model, the accuracy and efficiency of the method were verified. The influence of the primary substructure external nodes selection, the residual structure location distribution and the primary substructure size selection on the repetitive substructure modeling and analysis results was analyzed. The following conclusions are drawn:For the structure of stitched sandwich panel with repetitive unit cell, the dynamic structure modeling method of the repetitive substructure is used, the selection of the residual structure is not unique. And the more of the number of external nodes of the primary substructure, the less of the repeated mapping process, the higher of the calculation accuracy and computational efficiency. The repetitive substructure modeling method of the composite structure can improve the dynamic analysis efficiency of the composite structure when the external node selection ratio of the initial substructure is 50%.
According to the repeatability of the composite cell structure, a dynamic modeling method for stitched sandwich panel based on the repetitive substructure was proposed. The primary substructure and the residual structure were constructed by using the precise finite element model of the composite unit cell. The repetitive substructure was obtained by mapping the spatial position relation. All the substructures were assembled on the residual structure to realize the dynamic modeling and analysis of the repetitive substructure of the composite. Taking the stitched sandwich panel as an example, the repetitive substructure modeling and dynamic characteristic analysis were carried out, and compared with the precise solid finite element model, the accuracy and efficiency of the method were verified. The influence of the primary substructure external nodes selection, the residual structure location distribution and the primary substructure size selection on the repetitive substructure modeling and analysis results was analyzed. The following conclusions are drawn:For the structure of stitched sandwich panel with repetitive unit cell, the dynamic structure modeling method of the repetitive substructure is used, the selection of the residual structure is not unique. And the more of the number of external nodes of the primary substructure, the less of the repeated mapping process, the higher of the calculation accuracy and computational efficiency. The repetitive substructure modeling method of the composite structure can improve the dynamic analysis efficiency of the composite structure when the external node selection ratio of the initial substructure is 50%.
