2019 Vol. 36, No. 12
2019, 36(12): 2735-2744.
doi: 10.13801/j.cnki.fhclxb.20190729.003
Abstract:
Epoxy resin-concrete is a new type of polymer concrete prepared by mixing epoxy resin, curing agent and aggregate. Fast growth of early strength is one of its excellent properties. In this paper, the uniaxial compression tests of epoxy resin-concrete at different ages were carried out to study the early compressive performance of epoxy resin-concrete. Test results show that the compressive strength of epoxy resin-concrete increases rapidly during the first 24 h curing age, and the compressive strength after curing 24 h can achieve 50.3 MPa. Considering the strength growth mechanism of epoxy resin-concrete and the stability of compressive strength after curing 72 h, a prediction model of early compressive strength of epoxy resin-concrete based on a nth order curing model for epoxy resin was established. The model has better prediction results compared with the classic CEB-FIP and ACI 209 models forconventional cement concrete. Based on the prediction model and experimental results of compressive strength, a uniaxial compression constitutive model of epoxy resin-concrete was established. This model can predict the compressive stress-strain relationship of epoxy resin-concrete at early-age.
Epoxy resin-concrete is a new type of polymer concrete prepared by mixing epoxy resin, curing agent and aggregate. Fast growth of early strength is one of its excellent properties. In this paper, the uniaxial compression tests of epoxy resin-concrete at different ages were carried out to study the early compressive performance of epoxy resin-concrete. Test results show that the compressive strength of epoxy resin-concrete increases rapidly during the first 24 h curing age, and the compressive strength after curing 24 h can achieve 50.3 MPa. Considering the strength growth mechanism of epoxy resin-concrete and the stability of compressive strength after curing 72 h, a prediction model of early compressive strength of epoxy resin-concrete based on a nth order curing model for epoxy resin was established. The model has better prediction results compared with the classic CEB-FIP and ACI 209 models forconventional cement concrete. Based on the prediction model and experimental results of compressive strength, a uniaxial compression constitutive model of epoxy resin-concrete was established. This model can predict the compressive stress-strain relationship of epoxy resin-concrete at early-age.
2019, 36(12): 2745-2755.
doi: 10.13801/j.cnki.fhclxb.20190304.002
Abstract:
Based on the high-order shear theory, the theoretical study on the bending characteristic of composite grid sandwich panels with soft core materials was carried out. Based on the energy method, the calculation formula of the equivalent elastic parameters of composite grid with soft core material was derived. Based on the high-order shear bending theory, the bending differential equilibrium equation of the sandwich plate was derived, and the Navier method was used to give the theoretical solution of the bending of sandwich plate under distributed load with symmetrically laid upper and lower layers and four simple-supported sides. In the example, the theoretical solution of the typical grid sandwich plate was compared with the finite element simulation with the error of 7.1%, which verified the correctness of the theoretical method. The influence of the parameters such as span ratio of the sandwich panel, thickness of the grid, angle of the laminate composite layer and grid spacing on the bending deflection of a typical composite grid sandwich panel containing a soft core material was also analyzed.
Based on the high-order shear theory, the theoretical study on the bending characteristic of composite grid sandwich panels with soft core materials was carried out. Based on the energy method, the calculation formula of the equivalent elastic parameters of composite grid with soft core material was derived. Based on the high-order shear bending theory, the bending differential equilibrium equation of the sandwich plate was derived, and the Navier method was used to give the theoretical solution of the bending of sandwich plate under distributed load with symmetrically laid upper and lower layers and four simple-supported sides. In the example, the theoretical solution of the typical grid sandwich plate was compared with the finite element simulation with the error of 7.1%, which verified the correctness of the theoretical method. The influence of the parameters such as span ratio of the sandwich panel, thickness of the grid, angle of the laminate composite layer and grid spacing on the bending deflection of a typical composite grid sandwich panel containing a soft core material was also analyzed.
2019, 36(12): 2756-2763.
doi: 10.13801/j.cnki.fhclxb.20181119.003
Abstract:
Conductive rubber is a kind of key material and widely used in flexible electronics for its high elasticity and good conductivity. The rearrangement of the conductive filler may lead to the corresponding resistance change when the conductive rubber experiences loadings. In this study, the conductive rubber was prepared by filling Ni coated carbon fibers (CF-Ni) in polydimethylsiloxane (PDMS) matrix and the distribution of CF-Ni was observed. The static distribution of CF-Ni fiber filling in conductive rubber was observed and the calculation method of fiber orientation rate was constructed. The 3D printed samples were synchronously observed when the fillings were redistributed in the matrix under tensile loading. The results show that the CF-Ni fiber deflection along the direction of the tensile strain and the maximum deflection angle achieves to 20°. It is found that fiber orientation distribution and fiber deflection will affect the electrical properties of conductive rubber at different tensile strain. The maximum surface resistance variation of CF-Ni/PDMS is 600% with 60% dependent variable. The response of the resistance in CF-Ni/PDMS conductive rubber at different tensile strain builds a foundation for the preparation of flexible sensor.
Conductive rubber is a kind of key material and widely used in flexible electronics for its high elasticity and good conductivity. The rearrangement of the conductive filler may lead to the corresponding resistance change when the conductive rubber experiences loadings. In this study, the conductive rubber was prepared by filling Ni coated carbon fibers (CF-Ni) in polydimethylsiloxane (PDMS) matrix and the distribution of CF-Ni was observed. The static distribution of CF-Ni fiber filling in conductive rubber was observed and the calculation method of fiber orientation rate was constructed. The 3D printed samples were synchronously observed when the fillings were redistributed in the matrix under tensile loading. The results show that the CF-Ni fiber deflection along the direction of the tensile strain and the maximum deflection angle achieves to 20°. It is found that fiber orientation distribution and fiber deflection will affect the electrical properties of conductive rubber at different tensile strain. The maximum surface resistance variation of CF-Ni/PDMS is 600% with 60% dependent variable. The response of the resistance in CF-Ni/PDMS conductive rubber at different tensile strain builds a foundation for the preparation of flexible sensor.
2019, 36(12): 2764-2771.
doi: 10.13801/j.cnki.fhclxb.20190104.001
Abstract:
The lightning damage properties of carbon fiber reinforced polymer (CF/EP) laminates subjected to the single lightning impulse and multiple lightning component strikes with different combinations were experimentally evaluated to explore the flowing process and interaction mechanism of multiple continuous lightning components on CF/EP laminates. The experimental results indicate that CF/EP laminates suffer serious lightning damage, including fractures and erosion of carbon fibers, resin pyrolysis and layer delamination. The damage area and depth are approximately 2 790 mm2 and 1.28 mm in the "ABCD" test mode. In the multiple continuous lightning current test, the lightning damage depth of CF/EP is closely related to the impact force effect and the breakdown effect of lightning components A, B and D. The thermal effect of the lightning component C with long-duration and large amount of transferred charge contributes nearly 40% to the damage area. The combination and application sequence of multiple lightning components are important factors for evaluating the lightning damage of CF/EP laminates. The lightning damage effect of the single lightning impulse differs greatly from the lightning damage when the lightning component is a part of the multiple continuous lightning component sequence. The study on the damage effect of CF/EP under the multiple continuous lightning components can deepen the understanding of the lightning interaction process and provide experimental and theoretical basis for studying the mechanism of the lightning effect and the establishment of lightning test methods.
The lightning damage properties of carbon fiber reinforced polymer (CF/EP) laminates subjected to the single lightning impulse and multiple lightning component strikes with different combinations were experimentally evaluated to explore the flowing process and interaction mechanism of multiple continuous lightning components on CF/EP laminates. The experimental results indicate that CF/EP laminates suffer serious lightning damage, including fractures and erosion of carbon fibers, resin pyrolysis and layer delamination. The damage area and depth are approximately 2 790 mm2 and 1.28 mm in the "ABCD" test mode. In the multiple continuous lightning current test, the lightning damage depth of CF/EP is closely related to the impact force effect and the breakdown effect of lightning components A, B and D. The thermal effect of the lightning component C with long-duration and large amount of transferred charge contributes nearly 40% to the damage area. The combination and application sequence of multiple lightning components are important factors for evaluating the lightning damage of CF/EP laminates. The lightning damage effect of the single lightning impulse differs greatly from the lightning damage when the lightning component is a part of the multiple continuous lightning component sequence. The study on the damage effect of CF/EP under the multiple continuous lightning components can deepen the understanding of the lightning interaction process and provide experimental and theoretical basis for studying the mechanism of the lightning effect and the establishment of lightning test methods.
2019, 36(12): 2772-2778.
doi: 10.13801/j.cnki.fhclxb.20190324.001
Abstract:
Using differential geometry theory and the fourth-order Runge-Kutta methods to solve non-geodetic winding angle differential equation of T700 carbon fiber reinforced resin composite (CFRP) in cylinder head, a stable non-geodetic winding trajectory was obtained. Using the finite element simulation software to build the finite element model of T700 (CFRP) winding cylinder, the influence of different non-geodetic trajectories on the strength of T700 CFRP winding cylinder under working pressure was analyzed. The progressive damage model was used to analyze the law of burst pressure. For T700 CFRP winding cylinder with head of 50 mm, the T700 winding cylinder bearing capacity is the strongest when the slippage coefficient is 0.2, which is 7 MPa higher, about 6.4%, compared with T700 CFRP geodesic winding cylinder. For geodesic winding cylinder with head of 160 mm, the T700 CFRP winding cylinder bearing capacity is the strongest when the slippage coefficient is 0.2, which is 6 MPa higher, about 11.5%, compared with T700 CFRP geodesic winding cylinder. The results show that the optimized winding design can meet the basic requirements of the winding process, improve the structural mechanical properties of the T700 CFRP winding cylinder, and provide reasonable suggestions for the actual winding process.
Using differential geometry theory and the fourth-order Runge-Kutta methods to solve non-geodetic winding angle differential equation of T700 carbon fiber reinforced resin composite (CFRP) in cylinder head, a stable non-geodetic winding trajectory was obtained. Using the finite element simulation software to build the finite element model of T700 (CFRP) winding cylinder, the influence of different non-geodetic trajectories on the strength of T700 CFRP winding cylinder under working pressure was analyzed. The progressive damage model was used to analyze the law of burst pressure. For T700 CFRP winding cylinder with head of 50 mm, the T700 winding cylinder bearing capacity is the strongest when the slippage coefficient is 0.2, which is 7 MPa higher, about 6.4%, compared with T700 CFRP geodesic winding cylinder. For geodesic winding cylinder with head of 160 mm, the T700 CFRP winding cylinder bearing capacity is the strongest when the slippage coefficient is 0.2, which is 6 MPa higher, about 11.5%, compared with T700 CFRP geodesic winding cylinder. The results show that the optimized winding design can meet the basic requirements of the winding process, improve the structural mechanical properties of the T700 CFRP winding cylinder, and provide reasonable suggestions for the actual winding process.
2019, 36(12): 2779-2785.
doi: 10.13801/j.cnki.fhclxb.20190304.001
Abstract:
According to the vacuum assisted resin infusion (VARI) technology, the formation mechanism and elimination method of the penetration and defects in the wind turbine blades of glass fiber/epoxy resin composites prepared by VARI method were studied. The results show that when the environment temperature is 25℃, the initial mixing time is 100 min, and the viscosity of mixed resin is 250 mPas, the exothermic temperature and permeability of the resin are the best. The use of flow guiding medium can decrease the difficulty of penetration and shorten the molding time. Through using triaxial glass fiber stitched fabric as 6 layers and inserting a continuous felt as the flow guiding medium, the best flow guiding effect can be obtained, and the penetration effect will be consistent, which can effectively reduce the influence of edge effect on the penetration. The penetration and defects can be reduced by increasing the feed port position of resin in L7000 (from the blade root to the feed port at 17 cm) and L19000(from the blade root to the feed port at 19 cm), and adjusting the mold temperature to 28℃.
According to the vacuum assisted resin infusion (VARI) technology, the formation mechanism and elimination method of the penetration and defects in the wind turbine blades of glass fiber/epoxy resin composites prepared by VARI method were studied. The results show that when the environment temperature is 25℃, the initial mixing time is 100 min, and the viscosity of mixed resin is 250 mPas, the exothermic temperature and permeability of the resin are the best. The use of flow guiding medium can decrease the difficulty of penetration and shorten the molding time. Through using triaxial glass fiber stitched fabric as 6 layers and inserting a continuous felt as the flow guiding medium, the best flow guiding effect can be obtained, and the penetration effect will be consistent, which can effectively reduce the influence of edge effect on the penetration. The penetration and defects can be reduced by increasing the feed port position of resin in L7000 (from the blade root to the feed port at 17 cm) and L19000(from the blade root to the feed port at 19 cm), and adjusting the mold temperature to 28℃.
2019, 36(12): 2786-2794.
doi: 10.13801/j.cnki.fhclxb.20190313.001
Abstract:
Due to its light mass and high strength, carbon fibre reinforced plastics (CFRP) is increasingly used in automotive light mass design and manufacturing. To study CFRP panels and influencing factors of drawing of CFRP-A1 laminates and accelerate the industrialization of composite parts, the curing and exothermic process of CFRP was analyzed by differential scanning calorimetry(DSC) test. Then, CFRP sheets and layer CFRP-A1 laminate with unidirectional and woven prepreg were prepared by autoclave at different post cure temperatures. The Inspelkt table 100 material testing machine was used to carry out the drawing test on the above-mentioned plates. In order to improve the preparation efficiency, the aluminum alloy plate surface was processed by grinding, grinding and coating silane coupling agent, anodizing and coating silane coupling agent. Without curing by autoclave, aluminum alloy plate and unidirectional prepreg tape with orthogonally symmetrically layered were combined warm drawing tamping in an environmental chamber of an Inspekt table 100 material testing machine. The microstructure was observed by metallographic microscope and SEM to verify the impact of post-cure temperature, the deep drawing ambient temperature, the type of prepreg tape and the surface treatment of the aluminum alloy plate on drawing properties of CFRP and CFRP-A1 laminates. The experiment results show that it is beneficial to the secondary drawing formability of the sheet by appropriately reducing the post-cure temperature and increasing the drawing temperature. The woven prepreg can withstand pressure better than the unidirectional prepreg leading to high drawing quality. The surface treatment of anodizing and coating silane coupling agent can form denser and uniform micropores on the surface, the combination can form a better interface, which is conducive to drawing.
Due to its light mass and high strength, carbon fibre reinforced plastics (CFRP) is increasingly used in automotive light mass design and manufacturing. To study CFRP panels and influencing factors of drawing of CFRP-A1 laminates and accelerate the industrialization of composite parts, the curing and exothermic process of CFRP was analyzed by differential scanning calorimetry(DSC) test. Then, CFRP sheets and layer CFRP-A1 laminate with unidirectional and woven prepreg were prepared by autoclave at different post cure temperatures. The Inspelkt table 100 material testing machine was used to carry out the drawing test on the above-mentioned plates. In order to improve the preparation efficiency, the aluminum alloy plate surface was processed by grinding, grinding and coating silane coupling agent, anodizing and coating silane coupling agent. Without curing by autoclave, aluminum alloy plate and unidirectional prepreg tape with orthogonally symmetrically layered were combined warm drawing tamping in an environmental chamber of an Inspekt table 100 material testing machine. The microstructure was observed by metallographic microscope and SEM to verify the impact of post-cure temperature, the deep drawing ambient temperature, the type of prepreg tape and the surface treatment of the aluminum alloy plate on drawing properties of CFRP and CFRP-A1 laminates. The experiment results show that it is beneficial to the secondary drawing formability of the sheet by appropriately reducing the post-cure temperature and increasing the drawing temperature. The woven prepreg can withstand pressure better than the unidirectional prepreg leading to high drawing quality. The surface treatment of anodizing and coating silane coupling agent can form denser and uniform micropores on the surface, the combination can form a better interface, which is conducive to drawing.
2019, 36(12): 2795-2804.
doi: 10.13801/j.cnki.fhclxb.20190514.001
Abstract:
A calculation model based on uncertainty theory for relative uncertainty of bolt load distribution in carbon fiber X850/resin composite multi-bolt joints was proposed for the existing problem of indeterminate testing deviation of bolt load distribution. This problem was caused because of the different testing methods and bolt load distributions of composite joints in different testing processes, so both the widely used strain gauge method and the latest instrumented bolt method were investigated. The research shows that the bolt load distribution in single-lap joints cannot be tested by the strain gauge method, and the relative uncertainty of double-lap joints is more than 2.8% in usual and will increase with the increasing of the number of bolts and the sticking deviation angle of strain gauges. The relative uncertainty of both single-lap and double-lap joints is no more than 1.5% with arbitrary number of bolts in the instrumented bolt method.
A calculation model based on uncertainty theory for relative uncertainty of bolt load distribution in carbon fiber X850/resin composite multi-bolt joints was proposed for the existing problem of indeterminate testing deviation of bolt load distribution. This problem was caused because of the different testing methods and bolt load distributions of composite joints in different testing processes, so both the widely used strain gauge method and the latest instrumented bolt method were investigated. The research shows that the bolt load distribution in single-lap joints cannot be tested by the strain gauge method, and the relative uncertainty of double-lap joints is more than 2.8% in usual and will increase with the increasing of the number of bolts and the sticking deviation angle of strain gauges. The relative uncertainty of both single-lap and double-lap joints is no more than 1.5% with arbitrary number of bolts in the instrumented bolt method.
2019, 36(12): 2805-2814.
doi: 10.13801/j.cnki.fhclxb.20190402.004
Abstract:
The thickness of tubular polyester-ramie/epoxy nonwoven composites has a certain influence on the flow capacity and strength of the lining material after pipeline rehabilitation. Therefore, the calculation formulas of thickness and overcurrent capability were established based on manning equation and the design criterion of composite pipe. The formula for calculating the strength was also established. The response surface method was used to optimize the preparation process of polyester-ramie nonwovens. Based on the single factor, according to the Box-Behnken test design principle, the three factors of hybrid ratio, fiber web quantification and needle density were selected according to the regression analysis equation. To determine the influencing factors of each process, the thickness and strength of the polyester-ramie nonwovens were used as the response surface and the contour map. The optimum process conditions for the preparation of polyester-ramie nonwovens are as follows:the hybrid ratio is 0.8, the fiber web quantification is 600 g/m2 and the needle density is 300 needle/cm2. Under the process, the polyester-ramie nonwovens have a thickness of 4.14 mm, a longitudinal tensile strength of 2.81 MPa, and a transverse tensile strength of 1.72 MPa, which is close to the theoretical value, indicating that the response surface method has practical value. Combined with polyester-ramie/epoxy nonwoven composites, the thickness and strength were used to verify rationality of the calculation formulas such as thickness, overcurrent capability and strength. It is found that the strength of the thinner polyester-ramie/epoxy nonwoven composites can meet the pressure requirements of the lining for repairing the drainage or sewage pipeline under the premise of the over-flow capability of the pipeline after repair.
The thickness of tubular polyester-ramie/epoxy nonwoven composites has a certain influence on the flow capacity and strength of the lining material after pipeline rehabilitation. Therefore, the calculation formulas of thickness and overcurrent capability were established based on manning equation and the design criterion of composite pipe. The formula for calculating the strength was also established. The response surface method was used to optimize the preparation process of polyester-ramie nonwovens. Based on the single factor, according to the Box-Behnken test design principle, the three factors of hybrid ratio, fiber web quantification and needle density were selected according to the regression analysis equation. To determine the influencing factors of each process, the thickness and strength of the polyester-ramie nonwovens were used as the response surface and the contour map. The optimum process conditions for the preparation of polyester-ramie nonwovens are as follows:the hybrid ratio is 0.8, the fiber web quantification is 600 g/m2 and the needle density is 300 needle/cm2. Under the process, the polyester-ramie nonwovens have a thickness of 4.14 mm, a longitudinal tensile strength of 2.81 MPa, and a transverse tensile strength of 1.72 MPa, which is close to the theoretical value, indicating that the response surface method has practical value. Combined with polyester-ramie/epoxy nonwoven composites, the thickness and strength were used to verify rationality of the calculation formulas such as thickness, overcurrent capability and strength. It is found that the strength of the thinner polyester-ramie/epoxy nonwoven composites can meet the pressure requirements of the lining for repairing the drainage or sewage pipeline under the premise of the over-flow capability of the pipeline after repair.
2019, 36(12): 2815-2821.
doi: 10.13801/j.cnki.fhclxb.20190111.001
Abstract:
The natural frequencies and vibration modes of the bolt fixed sandwich composite structure with stiffeners were obtained using finite element method in while the surface layers were simulated as layerwise elements and the core layers were simulated as solid elements. The simulated results were verified through comparing with experimental results. The method of simulating boundary condition for the actual structure in finite element analysis is obtained. By comparing with the experimental results of steel structure, it is found that the first three-order natural frequencies are twice higher for the sandwich composite reinforced structure. The sandwich composite structure with stiffeners can greatly improve the stiffness of the whole structure and the vibration characteristics of the structure.
The natural frequencies and vibration modes of the bolt fixed sandwich composite structure with stiffeners were obtained using finite element method in while the surface layers were simulated as layerwise elements and the core layers were simulated as solid elements. The simulated results were verified through comparing with experimental results. The method of simulating boundary condition for the actual structure in finite element analysis is obtained. By comparing with the experimental results of steel structure, it is found that the first three-order natural frequencies are twice higher for the sandwich composite reinforced structure. The sandwich composite structure with stiffeners can greatly improve the stiffness of the whole structure and the vibration characteristics of the structure.
2019, 36(12): 2822-2832.
doi: 10.13801/j.cnki.fhclxb.20190304.003
Abstract:
In order to research multiobjective optimization for minimizing residual stress, porosity and maximizing interlaminar shear strength during winding of composite prepreg tapes, T300/epoxy resin preprepreg tape winding experiment with four factors and three levels based on Box-Behnken Design (BBD) principle was designed. Based on grey relational analysis (GRA) the multi-objective optimization problem was transformed into a single-objective optimization problem. The influence weights of residual stress, porosity and interlayer shear strength on the grey relational grade(GRG) were determined by principal component analysis(PCA). Through regression analysis of the experimental data, a second-order prediction model of GRG and main winding process parameters was established. The effects of process parameters on residual stress, porosity, interlaminar shear strength and GRG were analyzed, and the optimum scheme of winding process parameters was determined. Response surface methodology (RSM) was used to solve the optimization problem of process parameters and the winding experiment of prepreg tape was carried out. The results show that the optimal combination of the process parameters obtained by this optimization method can effectively improve the residual stress, porosity and interlaminar shear strength, and improve the performance of preg tape winding products.
In order to research multiobjective optimization for minimizing residual stress, porosity and maximizing interlaminar shear strength during winding of composite prepreg tapes, T300/epoxy resin preprepreg tape winding experiment with four factors and three levels based on Box-Behnken Design (BBD) principle was designed. Based on grey relational analysis (GRA) the multi-objective optimization problem was transformed into a single-objective optimization problem. The influence weights of residual stress, porosity and interlayer shear strength on the grey relational grade(GRG) were determined by principal component analysis(PCA). Through regression analysis of the experimental data, a second-order prediction model of GRG and main winding process parameters was established. The effects of process parameters on residual stress, porosity, interlaminar shear strength and GRG were analyzed, and the optimum scheme of winding process parameters was determined. Response surface methodology (RSM) was used to solve the optimization problem of process parameters and the winding experiment of prepreg tape was carried out. The results show that the optimal combination of the process parameters obtained by this optimization method can effectively improve the residual stress, porosity and interlaminar shear strength, and improve the performance of preg tape winding products.
2019, 36(12): 2833-2842.
doi: 10.13801/j.cnki.fhclxb.20190117.001
Abstract:
Considering radial delamination of fiber winding composite flywheel at high speed, an annular plain woven fabric with both circumferential and radial reinforcement was proposed, and the prominent feature of new texture was that the circular yarn was continuously woven by a single fiber bundle. The representative volume unit cell with "flat spindle" section was established to deal with the differences between bidirectional yarn profiles. By means of structural similarity between sectorial and rectangular unit cell, constraint conditions for isoparametric weaving were defined. The volume averaging method was used to predict effective elastic parameters for sectorial unit cell of ring fabric. Based on the idea of multi-layered segmentation of rims, the stress and deformation characteristics of woven flywheel under rotating load and correlative influencing parameters were analyzed. The theoretical displacement shows good agreement with radial deformation measurement results using circles marking method. The maximum tangential speed of woven flywheel achieves 889 m/s, and the corresponding energy density reaches 63.7 Wh/kg. Both theoretical analysis and experimental results prove that the bidirectional reinforcement theory of circular texture is practicable. And woven composite flywheel is well promising in technological process to achieve higher rotation speed than traditional winding ones.
Considering radial delamination of fiber winding composite flywheel at high speed, an annular plain woven fabric with both circumferential and radial reinforcement was proposed, and the prominent feature of new texture was that the circular yarn was continuously woven by a single fiber bundle. The representative volume unit cell with "flat spindle" section was established to deal with the differences between bidirectional yarn profiles. By means of structural similarity between sectorial and rectangular unit cell, constraint conditions for isoparametric weaving were defined. The volume averaging method was used to predict effective elastic parameters for sectorial unit cell of ring fabric. Based on the idea of multi-layered segmentation of rims, the stress and deformation characteristics of woven flywheel under rotating load and correlative influencing parameters were analyzed. The theoretical displacement shows good agreement with radial deformation measurement results using circles marking method. The maximum tangential speed of woven flywheel achieves 889 m/s, and the corresponding energy density reaches 63.7 Wh/kg. Both theoretical analysis and experimental results prove that the bidirectional reinforcement theory of circular texture is practicable. And woven composite flywheel is well promising in technological process to achieve higher rotation speed than traditional winding ones.
2019, 36(12): 2843-2850.
doi: 10.13801/j.cnki.fhclxb.20190305.002
Abstract:
Python language was used to redevelop ABAQUS to generate 2D plane strain model with randomly distributed chopped carbon fibers. The representative volume element(RVE) was created and meshed with Hypermesh. In order to ensure the uniform coordination of the stress field of the RVE, the numerical simulation analysis of the tensile properties was under periodic boundary conditions, and the change trend of the effect of fiber length on the elastic modulus of the sheet molding compound was studied. The results verify that the tensile modulus of chopped carbon fiber/vinyl ester resin sheet molding compounds increases first and then decreases gradually with the increase of fiber length, and it is right to use Python-ABAQUS to establish a 2D plane strain RVE model. This study provides theoretical and experimental basis for the application of sheet molding compound in the automotive lightmass industry.
Python language was used to redevelop ABAQUS to generate 2D plane strain model with randomly distributed chopped carbon fibers. The representative volume element(RVE) was created and meshed with Hypermesh. In order to ensure the uniform coordination of the stress field of the RVE, the numerical simulation analysis of the tensile properties was under periodic boundary conditions, and the change trend of the effect of fiber length on the elastic modulus of the sheet molding compound was studied. The results verify that the tensile modulus of chopped carbon fiber/vinyl ester resin sheet molding compounds increases first and then decreases gradually with the increase of fiber length, and it is right to use Python-ABAQUS to establish a 2D plane strain RVE model. This study provides theoretical and experimental basis for the application of sheet molding compound in the automotive lightmass industry.
2019, 36(12): 2851-2859.
doi: 10.13801/j.cnki.fhclxb.20190305.003
Abstract:
A 3D microscopic unit-cell model of sand/resin was built based on the failure of sand/resin matrix fracture and sand/resin interface debonding. This model was employed to study the microscopic stress characteristics in resin sands, the damage of resin-bonded bridge, and the effect of microstructure (resin content, sand, sand particle size distribution, and the effective cross-sectional area ratio bonding bridge) on the tensile strength of sand/resin. A fracture mode based on energy mechanism i.e., cohesive behavior method was used to describe the debonding of sand/resin interface, and the extended finite element method (XFEM) was used to capture the matrix damage and crack propagation. The numerical results show that the proposed model can explicitly depict the microscopic fracture behavior of sand/resin and explain their fracture mechanisms. The valuable information involving the influence of the resin content, sand size, sand size grading, and the effective cross-sectional area ratio on the tensile strength (St) under the tensile loading is provided. This work can provide theoretical guidance for the resin sand optimization design.
A 3D microscopic unit-cell model of sand/resin was built based on the failure of sand/resin matrix fracture and sand/resin interface debonding. This model was employed to study the microscopic stress characteristics in resin sands, the damage of resin-bonded bridge, and the effect of microstructure (resin content, sand, sand particle size distribution, and the effective cross-sectional area ratio bonding bridge) on the tensile strength of sand/resin. A fracture mode based on energy mechanism i.e., cohesive behavior method was used to describe the debonding of sand/resin interface, and the extended finite element method (XFEM) was used to capture the matrix damage and crack propagation. The numerical results show that the proposed model can explicitly depict the microscopic fracture behavior of sand/resin and explain their fracture mechanisms. The valuable information involving the influence of the resin content, sand size, sand size grading, and the effective cross-sectional area ratio on the tensile strength (St) under the tensile loading is provided. This work can provide theoretical guidance for the resin sand optimization design.
2019, 36(12): 2860-2868.
doi: 10.13801/j.cnki.fhclxb.20190326.004
Abstract:
Effect of SiC particle(SiCP) gradation (45 μm and (45+100) μm) on the deformation and damage of 70vol% SiCP/Al composites was studied by an in situ X-ray imaging system. The strain fields of SiCP/Al composites at different deformation stages under quasi-static loading were calculated by the X-ray digital image correlation method (XDIC). The bulk-scale stress-strain curves show that the difference in the yield strength of SiCP/Al composites with different particle gradations is small. But the ductility of 45 μm SiCP/Al is higher than that of (45+100) μm SiCP/Al. Strain field mapping suggests that deformation and damage localizations appear earlier in (45+100) μm SiCP/Al than in 45 μm SiCP/Al, and the strain fields for (45+100) μm SiCP/Al are more heterogeneous in the later deformation stages. The reason is that strain localizations tend to nucleate around big particles which grow and coalesce to form macroscopic cracks, leading to an earlier failure of (100+45) μm SiCP/Al. Hence, optimizing the particle size distribution helps improve the ductility of particle-reinforced metal matrix composites. The postmortem analysis indicates that the fracture modes of the two SiCP/Al composites are both brittle, characterized by particle breakage and interfacial debonding in the fracture plane.
Effect of SiC particle(SiCP) gradation (45 μm and (45+100) μm) on the deformation and damage of 70vol% SiCP/Al composites was studied by an in situ X-ray imaging system. The strain fields of SiCP/Al composites at different deformation stages under quasi-static loading were calculated by the X-ray digital image correlation method (XDIC). The bulk-scale stress-strain curves show that the difference in the yield strength of SiCP/Al composites with different particle gradations is small. But the ductility of 45 μm SiCP/Al is higher than that of (45+100) μm SiCP/Al. Strain field mapping suggests that deformation and damage localizations appear earlier in (45+100) μm SiCP/Al than in 45 μm SiCP/Al, and the strain fields for (45+100) μm SiCP/Al are more heterogeneous in the later deformation stages. The reason is that strain localizations tend to nucleate around big particles which grow and coalesce to form macroscopic cracks, leading to an earlier failure of (100+45) μm SiCP/Al. Hence, optimizing the particle size distribution helps improve the ductility of particle-reinforced metal matrix composites. The postmortem analysis indicates that the fracture modes of the two SiCP/Al composites are both brittle, characterized by particle breakage and interfacial debonding in the fracture plane.
2019, 36(12): 2869-2877.
doi: 10.13801/j.cnki.fhclxb.20190109.003
Abstract:
Sparks plasma sintering (SPS) process was used to prepare copper matrix composites reinforced with different ratios of carbon nanotubes(CNTs) and TiB2 hybrid. Density, hardness, electrical conductivity, thermal conductivity and microstructure of the composites were compared and analyzed. To investigate the effects of hybrid ratios on the arc erosion behavior of CNTs-TiB2/Cu composites, electrical contact test was carried out at different currents. The results indicate gradual decrease in relative density, hardness, electrical conductivity and thermal conductivity, and an increase in separation of the copper grains with the increasing hybrid ratios. Arc erosion resistance of CNTs-TiB2/Cu composites is improved with appropriate ratios of CNTs to TiB2 under a certain current. The CNTs-TiB2/Cu composite with 4:1 hybrid ratio of CNTs to TiB2 has the lowest average making-arc-energy, average making-arc-durations and material transfer amounts at 5 A and 10 A, while the CNTs-TiB2/Cu composite with 1:4 hybrid ratio of CNTs to TiB2 has the lowest average making-arc-energy, average making-arc-durations and material transfer amounts at 15 A. The molten pool, pores and spread out of molten metal are formed on the cathode after arc erosion. Furthermore, molten pool, pores and spread out of molten metal decreases as the ratios of CNTs to TiB2 increase.
Sparks plasma sintering (SPS) process was used to prepare copper matrix composites reinforced with different ratios of carbon nanotubes(CNTs) and TiB2 hybrid. Density, hardness, electrical conductivity, thermal conductivity and microstructure of the composites were compared and analyzed. To investigate the effects of hybrid ratios on the arc erosion behavior of CNTs-TiB2/Cu composites, electrical contact test was carried out at different currents. The results indicate gradual decrease in relative density, hardness, electrical conductivity and thermal conductivity, and an increase in separation of the copper grains with the increasing hybrid ratios. Arc erosion resistance of CNTs-TiB2/Cu composites is improved with appropriate ratios of CNTs to TiB2 under a certain current. The CNTs-TiB2/Cu composite with 4:1 hybrid ratio of CNTs to TiB2 has the lowest average making-arc-energy, average making-arc-durations and material transfer amounts at 5 A and 10 A, while the CNTs-TiB2/Cu composite with 1:4 hybrid ratio of CNTs to TiB2 has the lowest average making-arc-energy, average making-arc-durations and material transfer amounts at 15 A. The molten pool, pores and spread out of molten metal are formed on the cathode after arc erosion. Furthermore, molten pool, pores and spread out of molten metal decreases as the ratios of CNTs to TiB2 increase.
2019, 36(12): 2878-2886.
doi: 10.13801/j.cnki.fhclxb.20190402.002
Abstract:
The (C/C)/ZrB2-SiC composites were prepared by slurry painting method and slurry impregnation method based on (C/C)/SiC composites. The ablation characteristics, phase composition and microstructure of the three kinds of composites were tested by oxyacetylene flame, SEM and EDS, respectively. The ablation mechanism was also investigated. The results indicate that compared with (C/C)/SiC composites, the (C/C)/ZrB2-SiC composites show better ablation resistance properties. As to the uncoated (C/C)/SiC composites, the linear ablation rate of the (C/C)/ZrB2-SiC composites is reduced by 33.3% and 15.4%, and the mass ablation rate reduces by 51.5% and 25.5% after ablation for 600 s and 1 000 s respectively, and the linear ablation rate of the micro-particle ZrB2 impregnation composites is reduced by 20% and 28.8%, and the mass ablation rate reduces by 42.4% and 52.3% after ablation for 600 s and 1 000 s respectively. A ZrO2-SiO2 glassy melting layer formed at high temperature plays an important role in antioxidant and antierosion, which induces in better ablation resistance properties of the (C/C)/ZrB2-SiC composites. The ablation mechanism is a synergistic effect of thermo-chemical ablation, thermo-physical ablation and mechanical erosion.
The (C/C)/ZrB2-SiC composites were prepared by slurry painting method and slurry impregnation method based on (C/C)/SiC composites. The ablation characteristics, phase composition and microstructure of the three kinds of composites were tested by oxyacetylene flame, SEM and EDS, respectively. The ablation mechanism was also investigated. The results indicate that compared with (C/C)/SiC composites, the (C/C)/ZrB2-SiC composites show better ablation resistance properties. As to the uncoated (C/C)/SiC composites, the linear ablation rate of the (C/C)/ZrB2-SiC composites is reduced by 33.3% and 15.4%, and the mass ablation rate reduces by 51.5% and 25.5% after ablation for 600 s and 1 000 s respectively, and the linear ablation rate of the micro-particle ZrB2 impregnation composites is reduced by 20% and 28.8%, and the mass ablation rate reduces by 42.4% and 52.3% after ablation for 600 s and 1 000 s respectively. A ZrO2-SiO2 glassy melting layer formed at high temperature plays an important role in antioxidant and antierosion, which induces in better ablation resistance properties of the (C/C)/ZrB2-SiC composites. The ablation mechanism is a synergistic effect of thermo-chemical ablation, thermo-physical ablation and mechanical erosion.
2019, 36(12): 2887-2893.
doi: 10.13801/j.cnki.fhclxb.20190416.003
Abstract:
In order to develop inorganic/organic dielectric composites with high energy storage density, the finite element method was adopt to study the effects of both morphologies and dielectric constant of fillers on the dielectric properties of inorganic/organic composites, including the ratio of dielectric constant of spherical filler to matrix (k), the size (100-300 nm) and the arrangement of spherical fillers, the aspect ratio of fiber fillers (α) and the sphericity of nanoplate fillers (β). The results show that the dielectric constant of composites doesn't change significantly when k exceeds 20. The composites will get large dielectric constant when the spherical fillers are chained along the direction of the electric field. Large electric displacement and large electric field appear at the interface between the spherical fillers and matrix, indicating that this arrangement is beneficial to the improvement of the dielectric constant of the composites, but weakens the breakdown resistance. When the spherical fillers are randomly distributed in the matrix, the sizes of fillers have little effect on the dielectric constant of composites. Fiber fillers with large α and the long axis along the direction of electric field will result in large electric displacement, which indicates this filler will improve dielectric constant of composites. The nanoplate fillers with small β bring out lower electric field at the interface, indicating that the composites possess higher breakdown resistance.
In order to develop inorganic/organic dielectric composites with high energy storage density, the finite element method was adopt to study the effects of both morphologies and dielectric constant of fillers on the dielectric properties of inorganic/organic composites, including the ratio of dielectric constant of spherical filler to matrix (k), the size (100-300 nm) and the arrangement of spherical fillers, the aspect ratio of fiber fillers (α) and the sphericity of nanoplate fillers (β). The results show that the dielectric constant of composites doesn't change significantly when k exceeds 20. The composites will get large dielectric constant when the spherical fillers are chained along the direction of the electric field. Large electric displacement and large electric field appear at the interface between the spherical fillers and matrix, indicating that this arrangement is beneficial to the improvement of the dielectric constant of the composites, but weakens the breakdown resistance. When the spherical fillers are randomly distributed in the matrix, the sizes of fillers have little effect on the dielectric constant of composites. Fiber fillers with large α and the long axis along the direction of electric field will result in large electric displacement, which indicates this filler will improve dielectric constant of composites. The nanoplate fillers with small β bring out lower electric field at the interface, indicating that the composites possess higher breakdown resistance.
2019, 36(12): 2894-2901.
doi: 10.13801/j.cnki.fhclxb.20190327.002
Abstract:
Quasi-static uniaxial tension and cyclic loading/unloading tests of the sutured 3D-C/SiC braided composites were carried out to research the effects of cycle loading/unloading behavior on the damage and inner energy dissipation. Through the fractography analysis of this material, the effect law of the strength change caused by cycle loading/unloading has been explored. The results show that the behavior of cycle loading/unloading will consume energy of interface between matrix and fiber bundle inside the material, resulting in damage to it, which reduces the load-bearing capacity of the material, and the area of hysteresis loop increases as the stress of each unloading point increases. The overall failure of this material is brittle failure, but the fracture of the sample shows obvious delamination under monotonous loading and cycle loading, while the fracture of the uniaxial tensile specimen is more uniform.
Quasi-static uniaxial tension and cyclic loading/unloading tests of the sutured 3D-C/SiC braided composites were carried out to research the effects of cycle loading/unloading behavior on the damage and inner energy dissipation. Through the fractography analysis of this material, the effect law of the strength change caused by cycle loading/unloading has been explored. The results show that the behavior of cycle loading/unloading will consume energy of interface between matrix and fiber bundle inside the material, resulting in damage to it, which reduces the load-bearing capacity of the material, and the area of hysteresis loop increases as the stress of each unloading point increases. The overall failure of this material is brittle failure, but the fracture of the sample shows obvious delamination under monotonous loading and cycle loading, while the fracture of the uniaxial tensile specimen is more uniform.
2019, 36(12): 2902-2911.
doi: 10.13801/j.cnki.fhclxb.20190109.001
Abstract:
Based on MSC. Marc finite element software, the densification process of single and two-press Cu-Cr powder particles was microcosmic simulated and analyzed. The effects of different pressing methods and friction coefficients on the particle density and morphology of Cu-Cr powder particles were studied. The results show that with the increase of friction coefficient, the densification degree of unidirectional compacted Cu-Cr powder particles is higher. Under the condition of friction coefficient of 0.5, the maximum density of unidirectional compacted Cu-Cr powder particles is 96.4040%. With the decrease of friction coefficient, the densification degree of the two-way compacted Cu-Cr powder particles is higher. Under ideal condition without friction, the densification of the two-press compacted Cu-Cr powder particles is up to 89.1630%. Under the same conditions (friction coefficient and compressive force), unidirectional compaction has higher fluidity and density than bi-directional compaction, and the strain difference of Cu particles is 1.3385. However, the particle size uniformity of bi-directional compaction is better than that of unidirectional compaction. The simulation results are in agreement with the experimental results, which verifies the accuracy of the model.
Based on MSC. Marc finite element software, the densification process of single and two-press Cu-Cr powder particles was microcosmic simulated and analyzed. The effects of different pressing methods and friction coefficients on the particle density and morphology of Cu-Cr powder particles were studied. The results show that with the increase of friction coefficient, the densification degree of unidirectional compacted Cu-Cr powder particles is higher. Under the condition of friction coefficient of 0.5, the maximum density of unidirectional compacted Cu-Cr powder particles is 96.4040%. With the decrease of friction coefficient, the densification degree of the two-way compacted Cu-Cr powder particles is higher. Under ideal condition without friction, the densification of the two-press compacted Cu-Cr powder particles is up to 89.1630%. Under the same conditions (friction coefficient and compressive force), unidirectional compaction has higher fluidity and density than bi-directional compaction, and the strain difference of Cu particles is 1.3385. However, the particle size uniformity of bi-directional compaction is better than that of unidirectional compaction. The simulation results are in agreement with the experimental results, which verifies the accuracy of the model.
2019, 36(12): 2912-2919.
doi: 10.13801/j.cnki.fhclxb.20190408.001
Abstract:
Based on the anisotropic damage evolution mechanisms of ceramic matrix composites under multiaxial stress, analytical model and methodology have been proposed for damage decoupling investigation, through which the interaction effects among damage components can be quantificationally characterized. Considering that the internal stresses of the load carrying material would be enhanced by mechanical damage, the parameter of effective stress was introduced in order to describe the degradation of load bearing capacity induced by micro-damage. Moreover, the maximum effective stress criterion and the quadratic effective stress criterion were suggested for strength failure discrimination under complex stress state. The damage evolution and strength failure analysis was performed with plain-weave C/SiC composites subjected to incremental cyclic tests of on-axis and off-axis tension and in-plane shear. Comparison between experimental and theoretical data demonstrates that the established strength theory is reasonable, and the predicted results are accurate.
Based on the anisotropic damage evolution mechanisms of ceramic matrix composites under multiaxial stress, analytical model and methodology have been proposed for damage decoupling investigation, through which the interaction effects among damage components can be quantificationally characterized. Considering that the internal stresses of the load carrying material would be enhanced by mechanical damage, the parameter of effective stress was introduced in order to describe the degradation of load bearing capacity induced by micro-damage. Moreover, the maximum effective stress criterion and the quadratic effective stress criterion were suggested for strength failure discrimination under complex stress state. The damage evolution and strength failure analysis was performed with plain-weave C/SiC composites subjected to incremental cyclic tests of on-axis and off-axis tension and in-plane shear. Comparison between experimental and theoretical data demonstrates that the established strength theory is reasonable, and the predicted results are accurate.
2019, 36(12): 2920-2931.
doi: 10.13801/j.cnki.fhclxb.20190327.001
Abstract:
Core shell conductive composite powders of TiO2 coated with SbxSn1-xO2 antimony-doped tin oxide(ATO) nanoparticles were prepared with urea as the precipitant by homogeneous precipitation. The as-prepared composite powders were characterized by SEM, EDS, HRTEM, XRD, XPS, electron paramagnetic resonance(EPR), FTIR and laser particle size analyzer(LPSA), respectively. Effects of several main experimental parameters on the resistivity of the TiO2@ATO powders were primarily investigated. A possible mechanism for coating of ATO nanoparticles on the surface of TiO2 microspheres was proposed. The results show that when the molar ratio of metal cation to urea for precipitation reaction is 1:10 at the temperature of 92℃, the release amount and rate of OH- are moderate. At the same time, SO42- was introduced as a catalyst to reduce the nucleation barrier of metal cations, in which the optimum molar ratio of SO42- to Cl- is 1:25. Uniform, continuous and compact shell layer of ATO of the obtained product is formed on the surface of the TiO2 with a thickness of approximately 15 nm. When completely covered, the resistivity of composite powders decreases first and then, when the molar ratio of Sn to Sb reaches 12:1, changes little with the increase of Sb doping amount. Under the optimum experimental conditions, TiO2@ATO has good electrical conductivity with the resistivity of 7.5 Ωcm.
Core shell conductive composite powders of TiO2 coated with SbxSn1-xO2 antimony-doped tin oxide(ATO) nanoparticles were prepared with urea as the precipitant by homogeneous precipitation. The as-prepared composite powders were characterized by SEM, EDS, HRTEM, XRD, XPS, electron paramagnetic resonance(EPR), FTIR and laser particle size analyzer(LPSA), respectively. Effects of several main experimental parameters on the resistivity of the TiO2@ATO powders were primarily investigated. A possible mechanism for coating of ATO nanoparticles on the surface of TiO2 microspheres was proposed. The results show that when the molar ratio of metal cation to urea for precipitation reaction is 1:10 at the temperature of 92℃, the release amount and rate of OH- are moderate. At the same time, SO42- was introduced as a catalyst to reduce the nucleation barrier of metal cations, in which the optimum molar ratio of SO42- to Cl- is 1:25. Uniform, continuous and compact shell layer of ATO of the obtained product is formed on the surface of the TiO2 with a thickness of approximately 15 nm. When completely covered, the resistivity of composite powders decreases first and then, when the molar ratio of Sn to Sb reaches 12:1, changes little with the increase of Sb doping amount. Under the optimum experimental conditions, TiO2@ATO has good electrical conductivity with the resistivity of 7.5 Ωcm.
2019, 36(12): 2932-2941.
doi: 10.13801/j.cnki.fhclxb.20190118.001
Abstract:
The normal concrete (NC) and glazed hollow bead insulation normal concrete (GHB/NC) were made for studying the process of performance degradation from normal temperature to 1 000℃, which including changes in apparent phenomena, loss of mass and compressive strength. Simultaneously, the adaptation of ultrasonic test in evaluating the performance of concrete after exposure to high temperature was investigated. The relationships between relative velocity, damage degree and temperature, compressive strength loss rate were comparative analyzed. The micro-structure changes of concrete specimens after exposure to different high temperatures were observed by SEM. The results show that it has good correlation of the parameters of relative velocity and damage degree in evaluating the performance of concrete after high temperature. The regression formula has a good fitting degree. With the rise of heat temperature, the internal damage of concrete is gradually intensified, cement hydrates decomposes and water disperses, which causes voids, cracks and interpenetration occurred on the surface and inside of the specimens. The bonding force between glazed hollow bead, coarse aggregates and cement paste is gradually weakened or even lost. These cause deterioration of macroscopic mechanical properties and increasing of compressive strength loss rate of GHB/NC and NC. After experiencing the high temperature of 800℃, the losses in compressive strength of NC and GHB/NC are 72.3% and 74.6%, and the bearing capacity is almost lost after exposure to 1 000℃.
The normal concrete (NC) and glazed hollow bead insulation normal concrete (GHB/NC) were made for studying the process of performance degradation from normal temperature to 1 000℃, which including changes in apparent phenomena, loss of mass and compressive strength. Simultaneously, the adaptation of ultrasonic test in evaluating the performance of concrete after exposure to high temperature was investigated. The relationships between relative velocity, damage degree and temperature, compressive strength loss rate were comparative analyzed. The micro-structure changes of concrete specimens after exposure to different high temperatures were observed by SEM. The results show that it has good correlation of the parameters of relative velocity and damage degree in evaluating the performance of concrete after high temperature. The regression formula has a good fitting degree. With the rise of heat temperature, the internal damage of concrete is gradually intensified, cement hydrates decomposes and water disperses, which causes voids, cracks and interpenetration occurred on the surface and inside of the specimens. The bonding force between glazed hollow bead, coarse aggregates and cement paste is gradually weakened or even lost. These cause deterioration of macroscopic mechanical properties and increasing of compressive strength loss rate of GHB/NC and NC. After experiencing the high temperature of 800℃, the losses in compressive strength of NC and GHB/NC are 72.3% and 74.6%, and the bearing capacity is almost lost after exposure to 1 000℃.
2019, 36(12): 2942-2949.
doi: 10.13801/j.cnki.fhclxb.20190314.004
Abstract:
Using an improved permeation test device, the effect of macro steel fiber(SF) content and load level on the permeability of concrete(NC) subjected to uniaxial compression was studied, and the data of test were fitted and analyzed. The effect of load level on damage of SF/NC was studied by ultrasonic testing. The results indicate that the permeability of NC is related to the load level, and there exists a threshold value for the applied load level. The addition of macro SF delays the threshold value, and the threshold value increases with fiber content within a certain range. When the fiber content is 0, 20, 40 and 60 kg/m3, the threshold value is about 0.6, 0.7, 0.7 and 0.8, respectively. The effect of load level on the ultrasonic pulse velocity of NC is similar to permeability coefficient, which can be used to evaluate the permeability of NC under uniaxial compression.
Using an improved permeation test device, the effect of macro steel fiber(SF) content and load level on the permeability of concrete(NC) subjected to uniaxial compression was studied, and the data of test were fitted and analyzed. The effect of load level on damage of SF/NC was studied by ultrasonic testing. The results indicate that the permeability of NC is related to the load level, and there exists a threshold value for the applied load level. The addition of macro SF delays the threshold value, and the threshold value increases with fiber content within a certain range. When the fiber content is 0, 20, 40 and 60 kg/m3, the threshold value is about 0.6, 0.7, 0.7 and 0.8, respectively. The effect of load level on the ultrasonic pulse velocity of NC is similar to permeability coefficient, which can be used to evaluate the permeability of NC under uniaxial compression.
2019, 36(12): 2950-2958.
doi: 10.13801/j.cnki.fhclxb.20190417.002
Abstract:
Pure SrTiO3, 0.5 mol% and 1.0 mol% vanadium doped SrTiO3 were synthesized through hydrothermal method (Noted as S-0, S-0.5, S-1.0 successively). Characterizations including XRD、SEM、BET specific surface area analysis、electron paramagnetic resonance(EPR)、XPS、FTIR、UV-vis absorption spectra and PL offered information about structural features and optical properties of as-prepared catalysts. NO photo-oxidation reaction and CO2 photoreduction reaction were employed to evaluate the photocatalytic activity of the catalysts. As the study results reveale, the visible-light response improves, and the density of oxygen vacancy decreases as vanadium was doped into Ti-site; S-0.5, the SrTiO3 sample with 0.5 mol% vanadium doping, shows a better catalytic activity than S-0 at the preliminary stage, but its catalytic activity decays subsequently. According to the characterizations and tests, it could be speculated that oxygen vacancy is the active site for the CO2 photoreduction reaction, and the insufficient of active sites resulting from the decrease of oxygen vacancy after vanadium doping is the key reason for the decay of photocatalytic activity.
Pure SrTiO3, 0.5 mol% and 1.0 mol% vanadium doped SrTiO3 were synthesized through hydrothermal method (Noted as S-0, S-0.5, S-1.0 successively). Characterizations including XRD、SEM、BET specific surface area analysis、electron paramagnetic resonance(EPR)、XPS、FTIR、UV-vis absorption spectra and PL offered information about structural features and optical properties of as-prepared catalysts. NO photo-oxidation reaction and CO2 photoreduction reaction were employed to evaluate the photocatalytic activity of the catalysts. As the study results reveale, the visible-light response improves, and the density of oxygen vacancy decreases as vanadium was doped into Ti-site; S-0.5, the SrTiO3 sample with 0.5 mol% vanadium doping, shows a better catalytic activity than S-0 at the preliminary stage, but its catalytic activity decays subsequently. According to the characterizations and tests, it could be speculated that oxygen vacancy is the active site for the CO2 photoreduction reaction, and the insufficient of active sites resulting from the decrease of oxygen vacancy after vanadium doping is the key reason for the decay of photocatalytic activity.
2019, 36(12): 2959-2967.
doi: 10.13801/j.cnki.fhclxb.20190402.003
Abstract:
The chitosan is used to improve the toughness and the adsorption of heavy metal ions of slag based geopolymer. The effects of chitosan content on the strength, flexural toughness and the adsorption of heavy metal ions of slag based geopolymer were focused, and FTIR, NMR, SEM and EDS was employed to explore the modification mechanisms of chitosan on slag based geopolymer. The results show that the 28 days flexural toughness coefficient of the slag based geopolymer with addition of 2% chitosan increases by 497.22% and its adsorption efficiency of Pb2+ and Cr3+ increases by 68.89%, 81.45%, respectively, compared with the blank sample. The chitosan can modify microstructures of the slag based geopolymer both in the molecular level, which is the formation of the C-O-Si bond and the reduction of polymerization degree of[SiO4], and in submicroscopic level, which is the formation of three-dimensional interpenetrating network structure of chitosan and slag based geopolymer. The high adsorption of chitosan and the increase of the C-S-H gel with low Ca/Si ratio are the main reason for markedly enhancement of the adsorption capacity of the slag based geopolymer.
The chitosan is used to improve the toughness and the adsorption of heavy metal ions of slag based geopolymer. The effects of chitosan content on the strength, flexural toughness and the adsorption of heavy metal ions of slag based geopolymer were focused, and FTIR, NMR, SEM and EDS was employed to explore the modification mechanisms of chitosan on slag based geopolymer. The results show that the 28 days flexural toughness coefficient of the slag based geopolymer with addition of 2% chitosan increases by 497.22% and its adsorption efficiency of Pb2+ and Cr3+ increases by 68.89%, 81.45%, respectively, compared with the blank sample. The chitosan can modify microstructures of the slag based geopolymer both in the molecular level, which is the formation of the C-O-Si bond and the reduction of polymerization degree of[SiO4], and in submicroscopic level, which is the formation of three-dimensional interpenetrating network structure of chitosan and slag based geopolymer. The high adsorption of chitosan and the increase of the C-S-H gel with low Ca/Si ratio are the main reason for markedly enhancement of the adsorption capacity of the slag based geopolymer.
2019, 36(12): 2968-2974.
doi: 10.13801/j.cnki.fhclxb.20190305.001
Abstract:
As an accompanying phenomenon, the acoustic emission of the concrete has memory of the stress-strain history, which could be used to evaluate the concrete damage history. The cyclic tensile failure experiment of the concrete specimen with central crack was conducted. Relationships between parameters of acoustic emission and cyclic loading process were analyzed. The acoustic emission damage mode of concrete under cyclic tension was established. The influence of initial width of crack on the Felicity rate was revealed. The results indicate that the Felicity rate of the concrete prisms gradually increase with the initial width of the crack under dynamic axial cyclic loading. The key outcomes of this article provide a new process of evaluating the concrete damage history with acoustic emission memory.
As an accompanying phenomenon, the acoustic emission of the concrete has memory of the stress-strain history, which could be used to evaluate the concrete damage history. The cyclic tensile failure experiment of the concrete specimen with central crack was conducted. Relationships between parameters of acoustic emission and cyclic loading process were analyzed. The acoustic emission damage mode of concrete under cyclic tension was established. The influence of initial width of crack on the Felicity rate was revealed. The results indicate that the Felicity rate of the concrete prisms gradually increase with the initial width of the crack under dynamic axial cyclic loading. The key outcomes of this article provide a new process of evaluating the concrete damage history with acoustic emission memory.
2019, 36(12): 2975-2983.
doi: 10.13801/j.cnki.fhclxb.20190215.001
Abstract:
The vibration and buckling behaviors of porous functionally graded material(FGM) beams under the action of axial mechanical load in hygrothermal environment were investigated by an extension of a n-th order generalized beam theory (GBT). The material properties were temperature-dependent and described by modified Voigt mixture rule with porosity. The free vibration and buckling equations of the system were obtained by using the macro-micro analytical approach and Hamilton principle, in which three types of hygro-thermal distribution through the thickness of a beam were assumed. Applying the Navier solution method, the solutions for the free vibration and buckling responses of FGM simply supported beams were presented. The availability and accuracy for the GBT were tested throughout the numerical results and herein the satisfactory values to n was proposed, which can also refine beam theories. The effects of three types of hygro-thermal distribution, coupling hygro-thermal-mechanical loads, porosity, material graded index and length-to-thickness ratio on the vibration and buckling behaviors of a FGM beam were discussed. The results show that frequency and buckling load of the structure decrease as both temperature and moisture rise, and different types of hygro-thermal distribution will lead to distinct effects on it. As the porosity of the material increases, the structural unitary stiffness will be weakened, while frequency and stability of the structure in hygro-thermal environment will increase. Hygro-thermal rise has a little effect for short and thick FGM porous beams but remarkable effect for long and thin ones on the frequency and stability.
The vibration and buckling behaviors of porous functionally graded material(FGM) beams under the action of axial mechanical load in hygrothermal environment were investigated by an extension of a n-th order generalized beam theory (GBT). The material properties were temperature-dependent and described by modified Voigt mixture rule with porosity. The free vibration and buckling equations of the system were obtained by using the macro-micro analytical approach and Hamilton principle, in which three types of hygro-thermal distribution through the thickness of a beam were assumed. Applying the Navier solution method, the solutions for the free vibration and buckling responses of FGM simply supported beams were presented. The availability and accuracy for the GBT were tested throughout the numerical results and herein the satisfactory values to n was proposed, which can also refine beam theories. The effects of three types of hygro-thermal distribution, coupling hygro-thermal-mechanical loads, porosity, material graded index and length-to-thickness ratio on the vibration and buckling behaviors of a FGM beam were discussed. The results show that frequency and buckling load of the structure decrease as both temperature and moisture rise, and different types of hygro-thermal distribution will lead to distinct effects on it. As the porosity of the material increases, the structural unitary stiffness will be weakened, while frequency and stability of the structure in hygro-thermal environment will increase. Hygro-thermal rise has a little effect for short and thick FGM porous beams but remarkable effect for long and thin ones on the frequency and stability.
2019, 36(12): 2984-2989.
doi: 10.13801/j.cnki.fhclxb.20190401.001
Abstract:
The structural dynamic characteristics analysis of hexagonal chiral structures with negative Poisson's ratio were studied in present research. In order to improve the structural stiffness performance of the hexagonal chiral element structure, an optimization formulation based on natural frequency parameters was established. By defining the weight coefficients corresponding to the natural frequencies of different orders, and the normalized model for the natural frequency parameter was established. Defining the chiral thickness and circular wall thickness of the element structure as design variable, the optimization equation was established. Finally, the structural optimization was carried out by introducing the genetic algorithm (GA). The results show that the natural frequency is obviously improved after optimization, which provides a certain reference value for the design and application of new materials for vibration and noise reduction.
The structural dynamic characteristics analysis of hexagonal chiral structures with negative Poisson's ratio were studied in present research. In order to improve the structural stiffness performance of the hexagonal chiral element structure, an optimization formulation based on natural frequency parameters was established. By defining the weight coefficients corresponding to the natural frequencies of different orders, and the normalized model for the natural frequency parameter was established. Defining the chiral thickness and circular wall thickness of the element structure as design variable, the optimization equation was established. Finally, the structural optimization was carried out by introducing the genetic algorithm (GA). The results show that the natural frequency is obviously improved after optimization, which provides a certain reference value for the design and application of new materials for vibration and noise reduction.
