2019 Vol. 36, No. 2
2019, 36(2): 269-276.
doi: 10.13801/j.cnki.fhclxb.20180907.004
Abstract:
Molecular simulation technology can explore the reaction mechanism and the microscopic parameters of internal structure of polymer systems from the atomic scale to discuss the factors affecting the macroscopic properties of polymer composites. In this paper, the material system design and structure-performance correlation of epoxy resin matrix composites were studied. The current research of molecular simulation technology for the cross-linked network structure of epoxy resin and the mechanism of nanoparticle reinforced epoxy resin systems were summarized. The latest research results of scientific issues such as micro-interface and structural design of carbon fiber/epoxy composites were introduced, and the guiding significance and research strategy of molecular simulation methods in the future development of high-performance polymer matrix composites were proposed.
Molecular simulation technology can explore the reaction mechanism and the microscopic parameters of internal structure of polymer systems from the atomic scale to discuss the factors affecting the macroscopic properties of polymer composites. In this paper, the material system design and structure-performance correlation of epoxy resin matrix composites were studied. The current research of molecular simulation technology for the cross-linked network structure of epoxy resin and the mechanism of nanoparticle reinforced epoxy resin systems were summarized. The latest research results of scientific issues such as micro-interface and structural design of carbon fiber/epoxy composites were introduced, and the guiding significance and research strategy of molecular simulation methods in the future development of high-performance polymer matrix composites were proposed.
2019, 36(2): 277-282.
doi: 10.13801/j.cnki.fhclxb.20180514.002
Abstract:
The high filtration efficiency and low flow resistance of air filtration materials were successfully prepared by composing electrospinning poly(vinylidene fluoride) (PVDF)-polyacrylonitrile (PAN) nanofibers with polypropylene(PP) melt-blown nonwoven. The influence of the PVDF to PAN mass ratio on the solution properties, morphology, specific surface area and filtration properties were investigated. The results show that when the PVDF to PAN mass ratio is 3:5, the solution has excellent spinnability and the well-distributed nanofibers with mean diameter of 0.59 μm can be formed. BET test result shows that it goes for nearly double the specific surface area when PVDF to PAN mass ratio decreases from 2:1 to 3:5. Besides, the filtration efficient and resistance determined by TSI 8130 filter were tested. Results reveal that electrospinning PVDF-PAN nanofibers can significantly improve the filtration performance of polypropylene melt-blown nonwovens, the filtration efficiency of PVDF-PAN/melt-blown PP nonwoven reaches to 99.95%, significantly higher than that of melt-blown nonwoven with 65%, the filtration resistance is 77 mm H2O (1 mm H2O=9.8 Pa), the filter quality factor reaches 0.0987, which is more higher than 0.0168 of melt-blow nonwoven. The filtration properties significantly enhance by composing electrosping PVDF-PAN nanofiber with melt-blow nonwoven.
The high filtration efficiency and low flow resistance of air filtration materials were successfully prepared by composing electrospinning poly(vinylidene fluoride) (PVDF)-polyacrylonitrile (PAN) nanofibers with polypropylene(PP) melt-blown nonwoven. The influence of the PVDF to PAN mass ratio on the solution properties, morphology, specific surface area and filtration properties were investigated. The results show that when the PVDF to PAN mass ratio is 3:5, the solution has excellent spinnability and the well-distributed nanofibers with mean diameter of 0.59 μm can be formed. BET test result shows that it goes for nearly double the specific surface area when PVDF to PAN mass ratio decreases from 2:1 to 3:5. Besides, the filtration efficient and resistance determined by TSI 8130 filter were tested. Results reveal that electrospinning PVDF-PAN nanofibers can significantly improve the filtration performance of polypropylene melt-blown nonwovens, the filtration efficiency of PVDF-PAN/melt-blown PP nonwoven reaches to 99.95%, significantly higher than that of melt-blown nonwoven with 65%, the filtration resistance is 77 mm H2O (1 mm H2O=9.8 Pa), the filter quality factor reaches 0.0987, which is more higher than 0.0168 of melt-blow nonwoven. The filtration properties significantly enhance by composing electrosping PVDF-PAN nanofiber with melt-blow nonwoven.
2019, 36(2): 283-292.
doi: 10.13801/j.cnki.fhclxb.20180510.001
Abstract:
The automated fiber placement(AFP) of continuous fiber reinforced thermoplastic composite(TPC) could realize the in-situ consolidation and offer the potential to manufacture large components, reduce cost and increase production rate. Desired quality of composite components depends intensively on the temperature field distribution, and the laser heating mechanism is very complicated because of the laser energy field is coupled with the temperature field generated by the absorption of laser, so the temperature history for laser heating of carbon fiber reinforced polyphenyl sulphide (CF/PPS) matrix composite in an automated fiber placement process was studied in the finite element simulation combined heat transfer model. Meanwhile, the temperature field measurement system was built to collect and memory the temperature history for layers. The study results show that a shadow zone is present prior to the bond zone and causes a rapid drop in temperature. The peak temperature of the bond zone gradually decreases belong with the increasing of placing speed and the faster the placement speed is, the smaller the peak temperature difference is and the bigger the difference between thermocouple and simulation is. With the increase of the laser output power, the peak temperature of the layers increases gradually. To improve the efficiency of the in-situ consolidation, the maximum speed is 0.75 m/s when the laser output power is 6kW. Because of the trend is similar by comparing peak temperature of the experimental results and the simulated results, the finite element simulation results are correct.
The automated fiber placement(AFP) of continuous fiber reinforced thermoplastic composite(TPC) could realize the in-situ consolidation and offer the potential to manufacture large components, reduce cost and increase production rate. Desired quality of composite components depends intensively on the temperature field distribution, and the laser heating mechanism is very complicated because of the laser energy field is coupled with the temperature field generated by the absorption of laser, so the temperature history for laser heating of carbon fiber reinforced polyphenyl sulphide (CF/PPS) matrix composite in an automated fiber placement process was studied in the finite element simulation combined heat transfer model. Meanwhile, the temperature field measurement system was built to collect and memory the temperature history for layers. The study results show that a shadow zone is present prior to the bond zone and causes a rapid drop in temperature. The peak temperature of the bond zone gradually decreases belong with the increasing of placing speed and the faster the placement speed is, the smaller the peak temperature difference is and the bigger the difference between thermocouple and simulation is. With the increase of the laser output power, the peak temperature of the layers increases gradually. To improve the efficiency of the in-situ consolidation, the maximum speed is 0.75 m/s when the laser output power is 6kW. Because of the trend is similar by comparing peak temperature of the experimental results and the simulated results, the finite element simulation results are correct.
2019, 36(2): 293-303.
doi: 10.13801/j.cnki.fhclxb.20180416.002
Abstract:
Graphene-nanosheet/polyethylene(GNS/LDPE) composite films with considerable orientation fabricated in sandwich structure were developed to investigate the electromagnetic interference shielding (EMIS) performance. The experimental results demonstrate that electrical property primarily determines EMIS function. The according theoretical calculations are performed based on well-materialized conductivity as for multilayer composite films to explored the essential mechanism of absorption and multiple-reflection for polymer-based graphene nanocomposite films. The improved EMIS performance could be obtained though modifying thickness, skin depth and electrical conductivity of active material in sandwich structure. The total shielding performance can be further improved from absorption shielding enhancement by enlarging shielding thickness. The optimized shielding efficiency achieves up to 31 dB, demonstrating significant shielding effectiveness of GNS/LDPE composite films. The shielding mechanism of nanocomposite sandwich structure presents fundamental regulation of designing high EMIS nanocomposites. The results reasonably suggest a effective technical approach to fulfill promising graphene/polymer nanocomposite films potentially in EMIS coating applications.
Graphene-nanosheet/polyethylene(GNS/LDPE) composite films with considerable orientation fabricated in sandwich structure were developed to investigate the electromagnetic interference shielding (EMIS) performance. The experimental results demonstrate that electrical property primarily determines EMIS function. The according theoretical calculations are performed based on well-materialized conductivity as for multilayer composite films to explored the essential mechanism of absorption and multiple-reflection for polymer-based graphene nanocomposite films. The improved EMIS performance could be obtained though modifying thickness, skin depth and electrical conductivity of active material in sandwich structure. The total shielding performance can be further improved from absorption shielding enhancement by enlarging shielding thickness. The optimized shielding efficiency achieves up to 31 dB, demonstrating significant shielding effectiveness of GNS/LDPE composite films. The shielding mechanism of nanocomposite sandwich structure presents fundamental regulation of designing high EMIS nanocomposites. The results reasonably suggest a effective technical approach to fulfill promising graphene/polymer nanocomposite films potentially in EMIS coating applications.
2019, 36(2): 304-314.
doi: 10.13801/j.cnki.fhclxb.20180402.005
Abstract:
The buckling and post-buckling analyses of carbon fiber reinforced epoxy-matrix composite (CFRP) arm under compressive and torsional loading conditions were addressed based on three-dimensional Puck failure criterion and phenomenological modulus degradation method. Taking into account the in-situ effect of the laminated structure and the effect of stress along the fiber direction on the transverse strength, a buckling analysis method considering progressive failure process of CFRP structures was established. The numerical implementation was realized by ANSYS material subroutine USERMAT. It is verified by comparing with the experimental results in the literature that, the new method can analyze the progressive failure process and post-buckling behavior of the composite structures with high accuracy. Furthermore, this method was used to analyze the buckling load and post-buckling behavior of a spacecraft composite arm under compressive and torsional loads.
The buckling and post-buckling analyses of carbon fiber reinforced epoxy-matrix composite (CFRP) arm under compressive and torsional loading conditions were addressed based on three-dimensional Puck failure criterion and phenomenological modulus degradation method. Taking into account the in-situ effect of the laminated structure and the effect of stress along the fiber direction on the transverse strength, a buckling analysis method considering progressive failure process of CFRP structures was established. The numerical implementation was realized by ANSYS material subroutine USERMAT. It is verified by comparing with the experimental results in the literature that, the new method can analyze the progressive failure process and post-buckling behavior of the composite structures with high accuracy. Furthermore, this method was used to analyze the buckling load and post-buckling behavior of a spacecraft composite arm under compressive and torsional loads.
2019, 36(2): 315-321.
doi: 10.13801/j.cnki.fhclxb.20180507.001
Abstract:
The injection-molded fiber reinforced thermoplastic composites are generally considered as isotropic material. However, the fibers manifest some degree orientation after injection molding, which makes the composite sample anisotropic. In order to reasonably predict the elastic modulus of such composites, the fiber length and orientation distribution in the injection-molded carbon fiber reinforced nylon 6 composites were tested and analyzed. The distribution of fiber orientation was obtained. Subsequently, combined with the mechanic model and stacking theory of unidirectional fiber reinforced composites, the theoretical model for predicting the elastic modulus of oriented fiber reinforced polymer composites was constructed. The theoretical results agree well with the tensile test ones, indicating that the accuracy of the prediction model is relatively high.
The injection-molded fiber reinforced thermoplastic composites are generally considered as isotropic material. However, the fibers manifest some degree orientation after injection molding, which makes the composite sample anisotropic. In order to reasonably predict the elastic modulus of such composites, the fiber length and orientation distribution in the injection-molded carbon fiber reinforced nylon 6 composites were tested and analyzed. The distribution of fiber orientation was obtained. Subsequently, combined with the mechanic model and stacking theory of unidirectional fiber reinforced composites, the theoretical model for predicting the elastic modulus of oriented fiber reinforced polymer composites was constructed. The theoretical results agree well with the tensile test ones, indicating that the accuracy of the prediction model is relatively high.
2019, 36(2): 322-329.
doi: 10.13801/j.cnki.fhclxb.20180409.001
Abstract:
The biaxial tensile mechanical properties of carbon fiber reinforced polymer(CFRP) cross-ply composite laminates with central hole were experimentally studied using the uniform thickness cruciform specimens with slots in the arms. Three biaxial load ratios were applied to study the effects of load ratio on the biaxial tensile strength and failure characteristics of CFRP cross-ply laminates. The results show that under the biaxial tensile loads, the interfaces between the plies with fibers cut off and their adjacent plies with continuous fibers are prone to delaminate, and resulting in the reduction of load bearing capacity of CFRP cross-ply laminate. Under an equal biaxial tensile load, the cracks initiate at the matrix between the cutting-off and the continuous fibers along the hole edge, resulting from the combined load of the transverse tension and longitudinal shear. Under an unequal biaxial tensile load, matrix crack initiates in the plies perpendicular to the load direction with a higher tensile velocity, and appears at the hole edge with a high stress concentration. With the increasing of the load ratios, the microstructure damage in the regions with a higher tensile velocity develops more rapid, and so does the corresponding stiffness reduction. The propagation direction of the main crack tends to be perpendicular to the tensile direction with a higher tensile velocity. The analysis of the strength envelope of the CFRP cross-ply laminate with central hole shows that the tensile strength in the direction with a higher tensile velocity increases gently with the increasing of load ratio.
The biaxial tensile mechanical properties of carbon fiber reinforced polymer(CFRP) cross-ply composite laminates with central hole were experimentally studied using the uniform thickness cruciform specimens with slots in the arms. Three biaxial load ratios were applied to study the effects of load ratio on the biaxial tensile strength and failure characteristics of CFRP cross-ply laminates. The results show that under the biaxial tensile loads, the interfaces between the plies with fibers cut off and their adjacent plies with continuous fibers are prone to delaminate, and resulting in the reduction of load bearing capacity of CFRP cross-ply laminate. Under an equal biaxial tensile load, the cracks initiate at the matrix between the cutting-off and the continuous fibers along the hole edge, resulting from the combined load of the transverse tension and longitudinal shear. Under an unequal biaxial tensile load, matrix crack initiates in the plies perpendicular to the load direction with a higher tensile velocity, and appears at the hole edge with a high stress concentration. With the increasing of the load ratios, the microstructure damage in the regions with a higher tensile velocity develops more rapid, and so does the corresponding stiffness reduction. The propagation direction of the main crack tends to be perpendicular to the tensile direction with a higher tensile velocity. The analysis of the strength envelope of the CFRP cross-ply laminate with central hole shows that the tensile strength in the direction with a higher tensile velocity increases gently with the increasing of load ratio.
2019, 36(2): 330-336.
doi: 10.13801/j.cnki.fhclxb.20180504.001
Abstract:
Fiber waviness is a common defect in the manufacturing process of composite laminate, which can decrease the stiffness and strength of composite structures. Effectively predict the failure strength of composite laminate with fiber waviness will produce positive effect. In this paper, an analysis method for calculating the failure strength of composite laminate that contain sine or cosine curved fiber waviness was presented. The failure strength was predicted based on laminated theory and Infinitesimal method using the previous model. In addition, Tsai-Wu's failure criterion was employed to calculating the initial strength damage for carbon fiber/epoxy resin composite laminate with fiber waviness. Comparison of the result of damage calculation between the analytical solutions and FEM results proves the accuracy of the method. The method presented in this paper has some advantages over FEM, such as less computation, easy formulation and modeling, higher computational efficiency, and is easy to quickly analyze and determine the damage location and damage strength of composite laminates with fiber waviness.
Fiber waviness is a common defect in the manufacturing process of composite laminate, which can decrease the stiffness and strength of composite structures. Effectively predict the failure strength of composite laminate with fiber waviness will produce positive effect. In this paper, an analysis method for calculating the failure strength of composite laminate that contain sine or cosine curved fiber waviness was presented. The failure strength was predicted based on laminated theory and Infinitesimal method using the previous model. In addition, Tsai-Wu's failure criterion was employed to calculating the initial strength damage for carbon fiber/epoxy resin composite laminate with fiber waviness. Comparison of the result of damage calculation between the analytical solutions and FEM results proves the accuracy of the method. The method presented in this paper has some advantages over FEM, such as less computation, easy formulation and modeling, higher computational efficiency, and is easy to quickly analyze and determine the damage location and damage strength of composite laminates with fiber waviness.
2019, 36(2): 337-346.
doi: 10.13801/j.cnki.fhclxb.20180502.004
Abstract:
In order to study the effect of wear on the macroscopic elastic constants of fabric liners made of polytetrafluoroethylene (PTFE) and fabric (Kevlar) as well as phenolic resin matrix, the microscopic geometric models of different wear stages were established in combination with the microstructure of the twill liner based on the mathematical model and the volume averaging algorithm in the micro mechanics of composites. Based on the geometrical parameters and the elastic constants of the fibers, the volume fraction and the correlation matrix of the fiber bundle and the matrix were calculated by MATLAB. Realizing the transformation of the elastic constants of the local coordinate system and the global coordinate system of the twill fabric liner, the elastic constant calculation model of the liner in the unworn stage was constructed, and the correctness of the method was proved by an example. The maximum error between theoretical and experimental values is 5.88%. On this basis, according to the structure and the wear depth of the liner, the wear was divided into six stages, and the elastic constants calculation models of different wear stages were established.
In order to study the effect of wear on the macroscopic elastic constants of fabric liners made of polytetrafluoroethylene (PTFE) and fabric (Kevlar) as well as phenolic resin matrix, the microscopic geometric models of different wear stages were established in combination with the microstructure of the twill liner based on the mathematical model and the volume averaging algorithm in the micro mechanics of composites. Based on the geometrical parameters and the elastic constants of the fibers, the volume fraction and the correlation matrix of the fiber bundle and the matrix were calculated by MATLAB. Realizing the transformation of the elastic constants of the local coordinate system and the global coordinate system of the twill fabric liner, the elastic constant calculation model of the liner in the unworn stage was constructed, and the correctness of the method was proved by an example. The maximum error between theoretical and experimental values is 5.88%. On this basis, according to the structure and the wear depth of the liner, the wear was divided into six stages, and the elastic constants calculation models of different wear stages were established.
2019, 36(2): 347-355.
doi: 10.13801/j.cnki.fhclxb.20180402.002
Abstract:
Taking into account the effect of the stitching threads on the bending and breaking of the in-plane fibers, the inclusion of stitch holes and resin-rich zones, the research focuses on the stitching reinforcement for the composite laminates containing a large hole (The ratio of laminate's width D and diameter R of the open-hole D/R<6). The finite element simulating calculation was carried out on the stitching reinforcement for composite laminates containing a large circular hole.On the tensile load, the effects of different stitch parameters (stitching needle distance, row spacing, edge distance, diameter and tension) on the mechanical properties of the laminate were calculated. And the damage caused by different stitch parameters to the in-plane fibers is regarded as equivalent to the expansion of the diameter of the hole. The finite element model of the equivalent modal without edge effect laminates was established, and the principle of the influences on the overall mechanical properties of the laminate by different stitch parameters was investigated. The less distance of the stitching needle, the poorer the mechanical properties of the laminates.When the stitching needle distance is less than 3.14 mm, the mechanical properties of the laminate decrease monotonically with the increase of the edge distance. When the stitching needle distance is between 3.14 mm and 6 mm, with the increase of the edge distance, the mechanical properties of the laminate present a trend similar to sine function, and the overall trend is increasing. When the needle distance is more than 6 mm, with the increase of the edge distance, the mechanical properties of the laminates increase monotonically. At the positions of 0° and 90° of the central hole, the defect of the stitch holes causes the early failure of the laminates easily.
Taking into account the effect of the stitching threads on the bending and breaking of the in-plane fibers, the inclusion of stitch holes and resin-rich zones, the research focuses on the stitching reinforcement for the composite laminates containing a large hole (The ratio of laminate's width D and diameter R of the open-hole D/R<6). The finite element simulating calculation was carried out on the stitching reinforcement for composite laminates containing a large circular hole.On the tensile load, the effects of different stitch parameters (stitching needle distance, row spacing, edge distance, diameter and tension) on the mechanical properties of the laminate were calculated. And the damage caused by different stitch parameters to the in-plane fibers is regarded as equivalent to the expansion of the diameter of the hole. The finite element model of the equivalent modal without edge effect laminates was established, and the principle of the influences on the overall mechanical properties of the laminate by different stitch parameters was investigated. The less distance of the stitching needle, the poorer the mechanical properties of the laminates.When the stitching needle distance is less than 3.14 mm, the mechanical properties of the laminate decrease monotonically with the increase of the edge distance. When the stitching needle distance is between 3.14 mm and 6 mm, with the increase of the edge distance, the mechanical properties of the laminate present a trend similar to sine function, and the overall trend is increasing. When the needle distance is more than 6 mm, with the increase of the edge distance, the mechanical properties of the laminates increase monotonically. At the positions of 0° and 90° of the central hole, the defect of the stitch holes causes the early failure of the laminates easily.
2019, 36(2): 356-361.
doi: 10.13801/j.cnki.fhclxb.20180427.003
Abstract:
The effect of irregular-void on transverse tensile properties of unidirectional fiber-reinforced composites was studied. Firstly, irregular-void random algorithms were programmed by C++. Secondly, the repeating unit cell (RUC) of the composites microstructure with random fibers and irregular-void was generated by Python. Then, the effect of irregular-void on transverse modulus and transverse tensile strength of unidirectional composites was simulated by the finite element method (FEM). It is found that void shape affects the initial damage, damage evolution and final damage of RUC. As void content increases, both transverse modulus and transverse tensile strength decrease. The effect of void content on transverse tensile strength is larger than on transverse modulus.
The effect of irregular-void on transverse tensile properties of unidirectional fiber-reinforced composites was studied. Firstly, irregular-void random algorithms were programmed by C++. Secondly, the repeating unit cell (RUC) of the composites microstructure with random fibers and irregular-void was generated by Python. Then, the effect of irregular-void on transverse modulus and transverse tensile strength of unidirectional composites was simulated by the finite element method (FEM). It is found that void shape affects the initial damage, damage evolution and final damage of RUC. As void content increases, both transverse modulus and transverse tensile strength decrease. The effect of void content on transverse tensile strength is larger than on transverse modulus.
2019, 36(2): 362-369.
doi: 10.13801/j.cnki.fhclxb.20180413.002
Abstract:
Flexural properties of hybrid composites reinforced by carbon fiber and basalt fiber were tested and the effects of hybrid ratio on the flexural properties were also analyzed, on the condition that basalt fiber was put on the compressive side. Three-point bending test was performed on the specimen to obtain the flexural properties and failure mode was observed by scanning electron microscopy. Compared with the pure CFRP specimen, flexural strength of the hybrid composites increases obviously, particularly as the hybrid ratio is 16.7% and 33.3%, the flexural strength increases by 12.4% and 15.2% accordingly. Meanwhile, the flexural modulus of hybrid composites decreases along with the increment of hybrid ratio. Fracture ductility enhances significantly and failure displacements of all hybrid composites and BFRP are higher than that of the pure CFRP. Furthermore, various failure modes can be observed on the compressive side, tensile side and middle layer of the hybrid composites.
Flexural properties of hybrid composites reinforced by carbon fiber and basalt fiber were tested and the effects of hybrid ratio on the flexural properties were also analyzed, on the condition that basalt fiber was put on the compressive side. Three-point bending test was performed on the specimen to obtain the flexural properties and failure mode was observed by scanning electron microscopy. Compared with the pure CFRP specimen, flexural strength of the hybrid composites increases obviously, particularly as the hybrid ratio is 16.7% and 33.3%, the flexural strength increases by 12.4% and 15.2% accordingly. Meanwhile, the flexural modulus of hybrid composites decreases along with the increment of hybrid ratio. Fracture ductility enhances significantly and failure displacements of all hybrid composites and BFRP are higher than that of the pure CFRP. Furthermore, various failure modes can be observed on the compressive side, tensile side and middle layer of the hybrid composites.
2019, 36(2): 370-379.
doi: 10.13801/j.cnki.fhclxb.20180427.002
Abstract:
From the viewpoint of dynamics, dynamic stiffness method was proposed to study the vibration-resistant performance degradation properties of fiber-reinforced composite thin plate in thermal environment. Firstly, with the consideration of the effect of pulse excitation load, the dynamic stiffness values in thermal environment were solved by using the principle of energy method, plate and shell theory and modal shape superposition method. Meanwhile, the analysis process of vibration-resistant performance degradation of composite thin plate in high-temperature environment was summarized. In addition, a TC500 fiber/epoxy composite plate was taken as a study object, and through the comparison of dynamic stiffness, natural frequency, damping and modal shape results were obtained by the theoretical calculation and experimental test. The feasibility of the proposed method and the reliability of such a dynamic index have been verified, which can be used to quantitatively evaluate the dynamic performance degradation of composite thin plate in thermal environment.
From the viewpoint of dynamics, dynamic stiffness method was proposed to study the vibration-resistant performance degradation properties of fiber-reinforced composite thin plate in thermal environment. Firstly, with the consideration of the effect of pulse excitation load, the dynamic stiffness values in thermal environment were solved by using the principle of energy method, plate and shell theory and modal shape superposition method. Meanwhile, the analysis process of vibration-resistant performance degradation of composite thin plate in high-temperature environment was summarized. In addition, a TC500 fiber/epoxy composite plate was taken as a study object, and through the comparison of dynamic stiffness, natural frequency, damping and modal shape results were obtained by the theoretical calculation and experimental test. The feasibility of the proposed method and the reliability of such a dynamic index have been verified, which can be used to quantitatively evaluate the dynamic performance degradation of composite thin plate in thermal environment.
2019, 36(2): 380-388.
doi: 10.13801/j.cnki.fhclxb.20180416.006
Abstract:
This research combines theory with experiment to study the influence of thermal environment on the vibration characteristics of fiber-reinforced resin composite thin plate. Firstly, with consideration of the influence of base excitation load, the analytical model of fiber-reinforced resin composite thin plate was established in thermal environment and the analytical formulas of calculating the natural frequencies, modal shapes, vibration responses and damping ratios were derived, so that the corresponding solving procedure of vibration characteristic of such composite plate can be summarized. Next, TC500 fiber/epoxy composite plate was taken as a study object and its vibration characteristic was measured based on the established vibration test system in thermal environment. It has been found from the experimental results that when the temperature increases from 20℃ to 200℃, the modal shapes of composite thin plate can hardly be changed, while the natural frequencies will decrease between the range of 2.3%-36.6%, the vibration responses will increase between the range of 15.3%-58.4% and damping property also shows the upward tendency, e.g. when the temperature reaches to 200℃, the first 6 damping ratios will rise from 13.9% to 56.4% compared with the ones at room temperature. Besides, by comparing the theoretically calculated frequencies, shapes, vibration responses and damping parameters with the corresponding experimental results in different thermal environments, there is a good agreement between them. Therefore, the correctness of the analysis method and its results have been verified.
This research combines theory with experiment to study the influence of thermal environment on the vibration characteristics of fiber-reinforced resin composite thin plate. Firstly, with consideration of the influence of base excitation load, the analytical model of fiber-reinforced resin composite thin plate was established in thermal environment and the analytical formulas of calculating the natural frequencies, modal shapes, vibration responses and damping ratios were derived, so that the corresponding solving procedure of vibration characteristic of such composite plate can be summarized. Next, TC500 fiber/epoxy composite plate was taken as a study object and its vibration characteristic was measured based on the established vibration test system in thermal environment. It has been found from the experimental results that when the temperature increases from 20℃ to 200℃, the modal shapes of composite thin plate can hardly be changed, while the natural frequencies will decrease between the range of 2.3%-36.6%, the vibration responses will increase between the range of 15.3%-58.4% and damping property also shows the upward tendency, e.g. when the temperature reaches to 200℃, the first 6 damping ratios will rise from 13.9% to 56.4% compared with the ones at room temperature. Besides, by comparing the theoretically calculated frequencies, shapes, vibration responses and damping parameters with the corresponding experimental results in different thermal environments, there is a good agreement between them. Therefore, the correctness of the analysis method and its results have been verified.
2019, 36(2): 389-399.
doi: 10.13801/j.cnki.fhclxb.20180502.007
Abstract:
Ultrasonic Lamb wave method is a common method to detect the damage of fiber reinforced plastics (FRP) plate. However, the anisotropy material property of FRP will have a great effect on the accuracy of damage location based on lamb wave method. In order to solve this problem, a time probability density method was proposed. The method is developed from traditional ellipse method and it considers the anisotropy property of FRP material. By taking account of the group velocity variation of A0 mode waves with different propagation directions, this method calculated the travel time of the reflection wave with any damage on FRP plate, and the time flight diagram could be obtained. By establishing the mapping relationship between the time of flight and the travel time of the actual damage reflected wave, a time probability density map could be obtained to characterize the probability of the existence of the damage. The result from numerical analysis and experimental study shows that the damage location error of this method can be reduced by more than 70% compared with that of the traditional ellipse method. This paper demonstrates the feasibility and accuracy of this method for the damage location of anisotropic FRP plates.
Ultrasonic Lamb wave method is a common method to detect the damage of fiber reinforced plastics (FRP) plate. However, the anisotropy material property of FRP will have a great effect on the accuracy of damage location based on lamb wave method. In order to solve this problem, a time probability density method was proposed. The method is developed from traditional ellipse method and it considers the anisotropy property of FRP material. By taking account of the group velocity variation of A0 mode waves with different propagation directions, this method calculated the travel time of the reflection wave with any damage on FRP plate, and the time flight diagram could be obtained. By establishing the mapping relationship between the time of flight and the travel time of the actual damage reflected wave, a time probability density map could be obtained to characterize the probability of the existence of the damage. The result from numerical analysis and experimental study shows that the damage location error of this method can be reduced by more than 70% compared with that of the traditional ellipse method. This paper demonstrates the feasibility and accuracy of this method for the damage location of anisotropic FRP plates.
2019, 36(2): 400-409.
doi: 10.13801/j.cnki.fhclxb.20180322.004
Abstract:
Fatigue tests for determining the preload relaxation of composite bolted joints under transverse cyclic loading and exploring the effects of fatigue damage and fretting wear on the preload decay were carried out. The Archard wear model and the ALE (Arbitrary Lagrangian-Eulerian) adaptive meshing technology were used to calculate the fretting wear between contact surfaces and were implemented in the finite element code ABAQUS with UMESHMOTION subroutine; a progressive fatigue damage model proposed by Shokrieh and Lessard was employed to perform the failure analysis, and material property degradation was programmed by using UMAT subroutine in ABAQUS. Based on this analysis, the mechanism of the preload changing under cyclic loads attributes to the coupling action of the fatigue damage in bolt connection, the bolt-hole elongation and the contact wear. Compared with the experimental results, the rationality and validity of the proposed method were verified.
Fatigue tests for determining the preload relaxation of composite bolted joints under transverse cyclic loading and exploring the effects of fatigue damage and fretting wear on the preload decay were carried out. The Archard wear model and the ALE (Arbitrary Lagrangian-Eulerian) adaptive meshing technology were used to calculate the fretting wear between contact surfaces and were implemented in the finite element code ABAQUS with UMESHMOTION subroutine; a progressive fatigue damage model proposed by Shokrieh and Lessard was employed to perform the failure analysis, and material property degradation was programmed by using UMAT subroutine in ABAQUS. Based on this analysis, the mechanism of the preload changing under cyclic loads attributes to the coupling action of the fatigue damage in bolt connection, the bolt-hole elongation and the contact wear. Compared with the experimental results, the rationality and validity of the proposed method were verified.
2019, 36(2): 410-417.
doi: 10.13801/j.cnki.fhclxb.20180327.002
Abstract:
In the drilling of carbon fibre reinforced plastic (CFRP) components, the cooling process is usually adopted to prolong the tool life and improve the machining quality. Among them, air cooling technology is widely used in actual processing because of its convenience. However, there is a lack of research about air cooling direction on tool wear and machining quality. In this paper, by controlling the flow direction of cooling air, an experimental study of drilling CFRP materials was carried out under dry drilling, forward jet cooling and reverse suction cooling. Meanwhile the change regulation of tool wear on the secondary cutting edge of the double apex angle drill tool was acquired. It is found that gas cooling can effectively restrain tool wear. Under the similar influence of exit temperature by gas cooling, the reverse suction cooling can better effectively restrain the tool wear than forward jet cooling. Furthermore, the inhibition effect of cooling conditions on drilling export damage was analysed, it is found that the tear of hole exit is less restrained by cooling and cooling ways. The height of burrs, however, is restrained obviously by the cooling ways. The reverse suction cooling can effectively reduce the height of burrs. It can be a suitable cooling process in drilling CFRP.
In the drilling of carbon fibre reinforced plastic (CFRP) components, the cooling process is usually adopted to prolong the tool life and improve the machining quality. Among them, air cooling technology is widely used in actual processing because of its convenience. However, there is a lack of research about air cooling direction on tool wear and machining quality. In this paper, by controlling the flow direction of cooling air, an experimental study of drilling CFRP materials was carried out under dry drilling, forward jet cooling and reverse suction cooling. Meanwhile the change regulation of tool wear on the secondary cutting edge of the double apex angle drill tool was acquired. It is found that gas cooling can effectively restrain tool wear. Under the similar influence of exit temperature by gas cooling, the reverse suction cooling can better effectively restrain the tool wear than forward jet cooling. Furthermore, the inhibition effect of cooling conditions on drilling export damage was analysed, it is found that the tear of hole exit is less restrained by cooling and cooling ways. The height of burrs, however, is restrained obviously by the cooling ways. The reverse suction cooling can effectively reduce the height of burrs. It can be a suitable cooling process in drilling CFRP.
2019, 36(2): 418-424.
doi: 10.13801/j.cnki.fhclxb.20180416.003
Abstract:
The Al matrix composite foams reinforced by carbon nanotubes (CNTs) were fabricated by space-holder method. The effects of test temperature, frequency, amplitude, as well as porosity and CNT content of foams on damping properties were investigated by thermomechanical analyzer, meanwhile the corresponding mechanisms were analyzed systematically. The results show that damping properties increase with the increment of porosity and amplitude, but decrease with the increase of frequency. When the range of environmental test temperature is 25-200℃, the loss factor changes a little. As the temperature is higher than 200℃, the loss factor increases evidently with the increasing of temperature. CNT reinforcement can obviously improve the damping properties. At room temperature, the loss factor of 3.0%CNTs/Al composite foams is 0.27, which is 3.71 times as large as that of Al foams. The damping mechanisms are mainly dislocation damping, grain boundary damping, pore damping, CNTs' inherence damping and CNTs-Al interface damping. It should be noted that the damping of inherence and interface plays an important role in enhancing the damping properties.
The Al matrix composite foams reinforced by carbon nanotubes (CNTs) were fabricated by space-holder method. The effects of test temperature, frequency, amplitude, as well as porosity and CNT content of foams on damping properties were investigated by thermomechanical analyzer, meanwhile the corresponding mechanisms were analyzed systematically. The results show that damping properties increase with the increment of porosity and amplitude, but decrease with the increase of frequency. When the range of environmental test temperature is 25-200℃, the loss factor changes a little. As the temperature is higher than 200℃, the loss factor increases evidently with the increasing of temperature. CNT reinforcement can obviously improve the damping properties. At room temperature, the loss factor of 3.0%CNTs/Al composite foams is 0.27, which is 3.71 times as large as that of Al foams. The damping mechanisms are mainly dislocation damping, grain boundary damping, pore damping, CNTs' inherence damping and CNTs-Al interface damping. It should be noted that the damping of inherence and interface plays an important role in enhancing the damping properties.
2019, 36(2): 425-433.
doi: 10.13801/j.cnki.fhclxb.20180416.001
Abstract:
The braided C/SiC composites with density of 1.65 g/cm3, 1.75 g/cm3 and 1.85 g/cm3 were tested to obtain the basic mechanical properties. The acoustic emission system was used to monitor the damage signals of the monotonic tensile test, and the characteristic parameter and K-cluster analysis of the acoustic emission signals after the noise reduction using wavelet method were analyzed. The difference of material density between the material damage mode, damage evolution process and failure modes was found by the analysis of SEM image. According to the distribution characteristics of the damage mode and acoustic emission events, the experimental acoustic emission signals were classified and analyzed, and the damage modes and damage evolution mechanisms of different density materials were studied, and the stress level, relative time and frequency of different damage modes are gradually increased with the increase of density. It is concluded that the material density can change the mechanical properties by influencing the damage degree and distribution area of matrix as well as the interfacial properties.
The braided C/SiC composites with density of 1.65 g/cm3, 1.75 g/cm3 and 1.85 g/cm3 were tested to obtain the basic mechanical properties. The acoustic emission system was used to monitor the damage signals of the monotonic tensile test, and the characteristic parameter and K-cluster analysis of the acoustic emission signals after the noise reduction using wavelet method were analyzed. The difference of material density between the material damage mode, damage evolution process and failure modes was found by the analysis of SEM image. According to the distribution characteristics of the damage mode and acoustic emission events, the experimental acoustic emission signals were classified and analyzed, and the damage modes and damage evolution mechanisms of different density materials were studied, and the stress level, relative time and frequency of different damage modes are gradually increased with the increase of density. It is concluded that the material density can change the mechanical properties by influencing the damage degree and distribution area of matrix as well as the interfacial properties.
2019, 36(2): 434-440.
doi: 10.13801/j.cnki.fhclxb.20180502.005
Abstract:
2D-SiCf/SiC composite is an important thermostructural material in aeronautics and astronautics fields. The statistical distributions of the tensile strength play a critical role in design, manufacture, examination and verification of the 2D-SiCf/SiC composite and the related components made of the composite. Therefore, the tensile strength of the 2D-SiCf/SiC was measured at room temperature (RT) and 1 200℃. SEM was employed to observe the fracture morphology. The result of the tensile strength was analyzed by Weibull, normal and lognormal distribution statistics and verified by Anderson-Darling method. The result shows the tensile strength at RT and 1 200℃ of 2D-SiCf/SiC can be better described by Weibull distribution than normal distribution and lognormal distribution. The tensile strength at 1 200℃ scatters is at larger range than that at RT according to Weibull model. The average tensile strength can be accurately predicted by the Weibull distribution. The fracture morphology confirms that distribution of the tensile strength of the 2D-SiCf/SiC is mainly caused by the fiber/matrix interfacial bonding strength and the fiber strength.
2D-SiCf/SiC composite is an important thermostructural material in aeronautics and astronautics fields. The statistical distributions of the tensile strength play a critical role in design, manufacture, examination and verification of the 2D-SiCf/SiC composite and the related components made of the composite. Therefore, the tensile strength of the 2D-SiCf/SiC was measured at room temperature (RT) and 1 200℃. SEM was employed to observe the fracture morphology. The result of the tensile strength was analyzed by Weibull, normal and lognormal distribution statistics and verified by Anderson-Darling method. The result shows the tensile strength at RT and 1 200℃ of 2D-SiCf/SiC can be better described by Weibull distribution than normal distribution and lognormal distribution. The tensile strength at 1 200℃ scatters is at larger range than that at RT according to Weibull model. The average tensile strength can be accurately predicted by the Weibull distribution. The fracture morphology confirms that distribution of the tensile strength of the 2D-SiCf/SiC is mainly caused by the fiber/matrix interfacial bonding strength and the fiber strength.
2019, 36(2): 441-449.
doi: 10.13801/j.cnki.fhclxb.20180427.001
Abstract:
C-(A)-S-H gels are not only affected by the composition of cement-based materials, but also affected by the environment. The effect of pH-values of Na2SO4 solution on the structure of C-(A)-S-H gels was studied by solid-state nuclear magnetic resonance (NMR) with deconvolution technique. The results show that the Al[4]/Si value of C-(A)-S-H gels decreases in sulfate attack process, due to Al3+ entering into gel early and coming out later. The decrease of the erosion solution pH value promotes the migration of Al[4] from C-S-H gels, which leads to the peak position of Al[4] shifting to a negative value. It is found that the average molecular chain length (MCL) of C-S-H gel increases due to the polymerization among[SiO4] ([AlO4]) tetrahedra. In addition, the degree of hydration of the pastes is improved with the decrease of the pH-value, which is not favorable to formation of AFt.
C-(A)-S-H gels are not only affected by the composition of cement-based materials, but also affected by the environment. The effect of pH-values of Na2SO4 solution on the structure of C-(A)-S-H gels was studied by solid-state nuclear magnetic resonance (NMR) with deconvolution technique. The results show that the Al[4]/Si value of C-(A)-S-H gels decreases in sulfate attack process, due to Al3+ entering into gel early and coming out later. The decrease of the erosion solution pH value promotes the migration of Al[4] from C-S-H gels, which leads to the peak position of Al[4] shifting to a negative value. It is found that the average molecular chain length (MCL) of C-S-H gel increases due to the polymerization among[SiO4] ([AlO4]) tetrahedra. In addition, the degree of hydration of the pastes is improved with the decrease of the pH-value, which is not favorable to formation of AFt.
2019, 36(2): 450-460.
doi: 10.13801/j.cnki.fhclxb.20180423.002
Abstract:
The development of a new kind of thermal protection material which combines non-ablation, thermal insulation, light-weight and reliability is the core technology for the development of new hypersonic vehicle. The interfaces between different materials are the most serious areas of thermal mismatch. The design of the gradient layers is the key to the realization of the composite material. To improve the performances of the composite material, deterministic optimization of transitional form of material components of the gradient layers and the material size parameters was made by using simplex method and neighborhood cultivation multi-objective genetic algorithm. Six Sigma method was further used to optimize the performances of the composite material considering uncertainty of material properties and load conditions and taking the above optimal solution as initial value. The optimization result shows that the optimization strategy can effectively improve the optimization efficiency while obtaining the optimal material performance parameters that meet the requirement of material reliability, which is especially important for calculating complex optimization problems.
The development of a new kind of thermal protection material which combines non-ablation, thermal insulation, light-weight and reliability is the core technology for the development of new hypersonic vehicle. The interfaces between different materials are the most serious areas of thermal mismatch. The design of the gradient layers is the key to the realization of the composite material. To improve the performances of the composite material, deterministic optimization of transitional form of material components of the gradient layers and the material size parameters was made by using simplex method and neighborhood cultivation multi-objective genetic algorithm. Six Sigma method was further used to optimize the performances of the composite material considering uncertainty of material properties and load conditions and taking the above optimal solution as initial value. The optimization result shows that the optimization strategy can effectively improve the optimization efficiency while obtaining the optimal material performance parameters that meet the requirement of material reliability, which is especially important for calculating complex optimization problems.
2019, 36(2): 461-468.
doi: 10.13801/j.cnki.fhclxb.20180412.001
Abstract:
Due to the anisotropic characteristics of C/C composite pins, the loading direction effects on the shear strength and shear constitutive model based on the Weibull model were studied. Then the Weibull model was invited to analyze the statistic distribution of the shear strength, and the parameters were estimated by the least square method. Based on the failure mechanism of C/C composites, an elastic-damage constitutive model with Weibull distribution was proposed, and the parameters were estimated with experimental data. The results show that the two-parameter Weibull function can be used to characterize the statistic distribution of shear strength according to the Kolmogorov-Smirnov test, and the C/C composite pins show the highest shear strength along the 45° direction. The shear stiffness of C/C composite pins decreases with the increasing shear angle, which decreases from 19.46 kN/mm (0° direction) to 12.70 kN/mm (90° direction).
Due to the anisotropic characteristics of C/C composite pins, the loading direction effects on the shear strength and shear constitutive model based on the Weibull model were studied. Then the Weibull model was invited to analyze the statistic distribution of the shear strength, and the parameters were estimated by the least square method. Based on the failure mechanism of C/C composites, an elastic-damage constitutive model with Weibull distribution was proposed, and the parameters were estimated with experimental data. The results show that the two-parameter Weibull function can be used to characterize the statistic distribution of shear strength according to the Kolmogorov-Smirnov test, and the C/C composite pins show the highest shear strength along the 45° direction. The shear stiffness of C/C composite pins decreases with the increasing shear angle, which decreases from 19.46 kN/mm (0° direction) to 12.70 kN/mm (90° direction).
2019, 36(2): 469-481.
doi: 10.13801/j.cnki.fhclxb.20180611.001
Abstract:
This paper presents an experimental study on the axial compressive behavior of 36 heat-damaged square columns wrapped by basalt fiber-reinforced polymer (BFRP) sheets and 15 reference columns after different levels of heat damage. The test results indicate that the BFRP confinement can change the failure mode of heat-damaged square columns and significantly enhance the strength and deformation properties of these columns. For the heat-damaged columns wrapped with three layers of BFRP sheets, the axial strengths of these columns after exposuring to 200℃, 400℃, 600℃ and 800℃ are increased by 48%, 130%, 206% and 389%, respectively; and the corresponding axial deformation increases are 433%, 344%, 319% and 251%, respectively. The typical ultimate stress and ultimate strain models for fiber-reinforced polymer (FRP)-confined undamaged concrete are not suitable for FRP-confined heat-damaged concrete. Through establishing the hydrostatic pressure balance equation of the cylindrical FRP membrane as well as proposing the volumetric strain energy models of confined concrete and BFRP sheets, the basic formulas defined for the axial ultimate stress and axial ultimate strain of FRP confined fire-damaged concrete columns are modified. The temperature-dependent variables in the proposed formulas were determined based on the presented experimental results, and therefore, design-oriented models were established for axial ultimate stress and axial ultimate strain of FRP-confined heat-damaged square concrete columns.
This paper presents an experimental study on the axial compressive behavior of 36 heat-damaged square columns wrapped by basalt fiber-reinforced polymer (BFRP) sheets and 15 reference columns after different levels of heat damage. The test results indicate that the BFRP confinement can change the failure mode of heat-damaged square columns and significantly enhance the strength and deformation properties of these columns. For the heat-damaged columns wrapped with three layers of BFRP sheets, the axial strengths of these columns after exposuring to 200℃, 400℃, 600℃ and 800℃ are increased by 48%, 130%, 206% and 389%, respectively; and the corresponding axial deformation increases are 433%, 344%, 319% and 251%, respectively. The typical ultimate stress and ultimate strain models for fiber-reinforced polymer (FRP)-confined undamaged concrete are not suitable for FRP-confined heat-damaged concrete. Through establishing the hydrostatic pressure balance equation of the cylindrical FRP membrane as well as proposing the volumetric strain energy models of confined concrete and BFRP sheets, the basic formulas defined for the axial ultimate stress and axial ultimate strain of FRP confined fire-damaged concrete columns are modified. The temperature-dependent variables in the proposed formulas were determined based on the presented experimental results, and therefore, design-oriented models were established for axial ultimate stress and axial ultimate strain of FRP-confined heat-damaged square concrete columns.
2019, 36(2): 482-490.
doi: 10.13801/j.cnki.fhclxb.20180410.003
Abstract:
In order to investigate the influence of steel fibers on the biaxial bending properties of basalt fiber textile reinforced concrete, two-way slab test in accordance with EFNARC was introduced. The biaxial flexural properties of the basalt fiber textile reinforced concrete slab, the steel fiber reinforced concrete slab and the combined use of steel fiber and basalt fiber textile reinforced slab were compared. The slab without any reinforcement and the conventional steel mesh reinforced concrete slab were also studied as reference. The biaxial reinforcement of the basalt fiber mesh was analyzed and the feasibility of using steel fiber and basalt fiber mesh to replace the conventional steel mesh was studied. The results show that the inner force redistribution and the ultimate load of the slab increase obviously with the addition of the basalt fiber mesh, but the failure pattern of the slab still demonstrate brittle feature. The combined use of steel fiber and basalt fiber mesh illustrates positive hybrid effect, the toughness of the slab increases significantly. In the serviceability stage, the flexural properties of the slab reinforced with 30 kg/m3 steel fiber and basalt fiber mesh are higher than the conventional steel mesh reinforced slab, it means that the conventional steel mesh can be replaced by the combined use of the steel fiber and the basalt fiber mesh.
In order to investigate the influence of steel fibers on the biaxial bending properties of basalt fiber textile reinforced concrete, two-way slab test in accordance with EFNARC was introduced. The biaxial flexural properties of the basalt fiber textile reinforced concrete slab, the steel fiber reinforced concrete slab and the combined use of steel fiber and basalt fiber textile reinforced slab were compared. The slab without any reinforcement and the conventional steel mesh reinforced concrete slab were also studied as reference. The biaxial reinforcement of the basalt fiber mesh was analyzed and the feasibility of using steel fiber and basalt fiber mesh to replace the conventional steel mesh was studied. The results show that the inner force redistribution and the ultimate load of the slab increase obviously with the addition of the basalt fiber mesh, but the failure pattern of the slab still demonstrate brittle feature. The combined use of steel fiber and basalt fiber mesh illustrates positive hybrid effect, the toughness of the slab increases significantly. In the serviceability stage, the flexural properties of the slab reinforced with 30 kg/m3 steel fiber and basalt fiber mesh are higher than the conventional steel mesh reinforced slab, it means that the conventional steel mesh can be replaced by the combined use of the steel fiber and the basalt fiber mesh.
2019, 36(2): 491-497.
doi: 10.13801/j.cnki.fhclxb.20180413.004
Abstract:
In order to study the effects of different fibers (steel fiber (SF), macro polypropylene fiber (Macro-PP) and micro polypropylene fiber (Micro-PP) on the permeability of fractured concrete under loading, different cracks(50-200 μm) were introduced by splitting test. The effects of different fibers on the crack width and tortuosity after unloading were compared. The influence of different fiber types, dosage and hybrid methods on the permeability of concrete with different crack width under load was analyzed by using the permeability test setup. It is found that the permeability decreases by 95.7%, if the steel fiber content increases from 25 kg/m3 up to 55 kg/m3. Compared with single-doped SF, the hybrid use of SF and macro-PP fibers indicates clear positive composite effect on the permeability; It has little change in permeability of cracked concrete reinforces with SF, micro-PP fiber and the combination of both fibers. The investigation demonstrates that the micro-PP fibers show low effect on restriction of the structural crack and the permeability. Steel fibers and macro-PP fibers restrictes the expansion of cracks effectively, increases the tortuosity of crack surface greatly, and reduces the permeability of cracked concrete greatly.
In order to study the effects of different fibers (steel fiber (SF), macro polypropylene fiber (Macro-PP) and micro polypropylene fiber (Micro-PP) on the permeability of fractured concrete under loading, different cracks(50-200 μm) were introduced by splitting test. The effects of different fibers on the crack width and tortuosity after unloading were compared. The influence of different fiber types, dosage and hybrid methods on the permeability of concrete with different crack width under load was analyzed by using the permeability test setup. It is found that the permeability decreases by 95.7%, if the steel fiber content increases from 25 kg/m3 up to 55 kg/m3. Compared with single-doped SF, the hybrid use of SF and macro-PP fibers indicates clear positive composite effect on the permeability; It has little change in permeability of cracked concrete reinforces with SF, micro-PP fiber and the combination of both fibers. The investigation demonstrates that the micro-PP fibers show low effect on restriction of the structural crack and the permeability. Steel fibers and macro-PP fibers restrictes the expansion of cracks effectively, increases the tortuosity of crack surface greatly, and reduces the permeability of cracked concrete greatly.
2019, 36(2): 498-505.
doi: 10.13801/j.cnki.fhclxb.20180330.001
Abstract:
Nano-SiO2(NS) has very strong pozzolanic activity, nucleation effect and filling effect, so using nano-SiO2 to improve the performance of cement-based materials has become a hot research topic of many scholars. This topic studied the effect of different dosage of NS on the strength and durability of lightweight aggregate concrete. The effects of NS on the macrostructure and microstructure of concrete were summarized and analyzed by testing the mechanical properties (compressive and flexural resistance) and chloride ion permeability of lightweight aggregate concrete, as well as the SEM and EDS test methods. The results show that NS can effectively improve the mechanical properties of lightweight aggregate concrete at appropriate dosage. The compressive strength and flexural strength of 28 d were 21.6% and 46.2% higher than that of the blank group concrete respectively. The results of chloride ion penetration show that the resistance to chloride ion permeability of lightweight aggregate concrete increases linearly with the increase of the content of nano-SiO2. Concrete interface transition zone (ITZ) has also undergone significant changes, its thickness decreases, the morphology is also more dense. The ratio of calcium to silicon in ITZ decreases with the increase of the amount of NS, which indicates that the C-S-H gel of hydration product increases and Ca(OH)2 is consumed in this region, resulting in a dense transition zone, which is conducive to the increase of the strength.
Nano-SiO2(NS) has very strong pozzolanic activity, nucleation effect and filling effect, so using nano-SiO2 to improve the performance of cement-based materials has become a hot research topic of many scholars. This topic studied the effect of different dosage of NS on the strength and durability of lightweight aggregate concrete. The effects of NS on the macrostructure and microstructure of concrete were summarized and analyzed by testing the mechanical properties (compressive and flexural resistance) and chloride ion permeability of lightweight aggregate concrete, as well as the SEM and EDS test methods. The results show that NS can effectively improve the mechanical properties of lightweight aggregate concrete at appropriate dosage. The compressive strength and flexural strength of 28 d were 21.6% and 46.2% higher than that of the blank group concrete respectively. The results of chloride ion penetration show that the resistance to chloride ion permeability of lightweight aggregate concrete increases linearly with the increase of the content of nano-SiO2. Concrete interface transition zone (ITZ) has also undergone significant changes, its thickness decreases, the morphology is also more dense. The ratio of calcium to silicon in ITZ decreases with the increase of the amount of NS, which indicates that the C-S-H gel of hydration product increases and Ca(OH)2 is consumed in this region, resulting in a dense transition zone, which is conducive to the increase of the strength.
2019, 36(2): 506-513.
doi: 10.13801/j.cnki.fhclxb.20180403.001
Abstract:
The deformation of cement sheath is often inconsistent with that of casing and formation, which leads to the failures of zonal isolation. In order to solve the problems, a kind of styrene butadiene rubber latex possessing good stability was synthesized by grafting 2-acrylamido-2-methyl-propane sulfonic acid and styrene to the liquid polybutadiene with low molecular weight via seed-emulsion polymerization. The structure and properties characteristics indicate that TEL-100L latex possesses good thermal stability and perfect core-shell structure. For oil well cement stone, the evaluations of mechanical property show that TEL-100L latex can significantly reduce the brittleness coefficient and elasticity modulus of cement stone, and improve its toughness and deformation ability. The exploration of toughening mechanism finds that TEL-100L latex can not only be adsorbed onto the cement grains surface by electrostatic attraction, but also can be cross connected with cement hydration system through the complexation with Ca2+, which leads to the formation of compact three-dimensional net structure and the improvement of toughness and deformation ability.
The deformation of cement sheath is often inconsistent with that of casing and formation, which leads to the failures of zonal isolation. In order to solve the problems, a kind of styrene butadiene rubber latex possessing good stability was synthesized by grafting 2-acrylamido-2-methyl-propane sulfonic acid and styrene to the liquid polybutadiene with low molecular weight via seed-emulsion polymerization. The structure and properties characteristics indicate that TEL-100L latex possesses good thermal stability and perfect core-shell structure. For oil well cement stone, the evaluations of mechanical property show that TEL-100L latex can significantly reduce the brittleness coefficient and elasticity modulus of cement stone, and improve its toughness and deformation ability. The exploration of toughening mechanism finds that TEL-100L latex can not only be adsorbed onto the cement grains surface by electrostatic attraction, but also can be cross connected with cement hydration system through the complexation with Ca2+, which leads to the formation of compact three-dimensional net structure and the improvement of toughness and deformation ability.
2019, 36(2): 514-521.
doi: 10.13801/j.cnki.fhclxb.20180328.004
Abstract:
The thermal stability of zwitterionic wormlike micelle(Z-WLM) solution with different nanocelluloses(NCs) was investigated. The effects of NCs concentration on the dynamic viscoelastic behavior, thixotropy and creep of Z-WLM were studied by linear rheological methods. The experimental result shows that a wormlike micelle(WLM) structure is formed by 4wt% erucy lamidopropyl betaine surfactant solution with many unique rheological properties, including shear thinning behavior, viscoelastic behavior, creep behavior and higher thixotropy recovery behavior, et al. Compared to other NCs, the NCs with high -COOH mass fraction and large aspect ratio possess better thickening efficiency. Moreover, the NCs can increase the Z-WLM solution's relaxation time and storage modulus, extend its thixotropy recovery time of shear viscosity and dynamic modulus, improve its creep recovery performance and thermal stability, which can use as a stimulation fluid in high temperature reservoirs from 70℃ to 100℃. With the increase of NCs concentration, the viscoelasticity and creep recovery performance of composite systems are increased and its thixotropy recovery performance is decreased.
The thermal stability of zwitterionic wormlike micelle(Z-WLM) solution with different nanocelluloses(NCs) was investigated. The effects of NCs concentration on the dynamic viscoelastic behavior, thixotropy and creep of Z-WLM were studied by linear rheological methods. The experimental result shows that a wormlike micelle(WLM) structure is formed by 4wt% erucy lamidopropyl betaine surfactant solution with many unique rheological properties, including shear thinning behavior, viscoelastic behavior, creep behavior and higher thixotropy recovery behavior, et al. Compared to other NCs, the NCs with high -COOH mass fraction and large aspect ratio possess better thickening efficiency. Moreover, the NCs can increase the Z-WLM solution's relaxation time and storage modulus, extend its thixotropy recovery time of shear viscosity and dynamic modulus, improve its creep recovery performance and thermal stability, which can use as a stimulation fluid in high temperature reservoirs from 70℃ to 100℃. With the increase of NCs concentration, the viscoelasticity and creep recovery performance of composite systems are increased and its thixotropy recovery performance is decreased.
2019, 36(2): 522-532.
doi: 10.13801/j.cnki.fhclxb.20180410.001
Abstract:
Tire is a kind of rubber-cord reinforced composite structure. Gough stiffness derived by using a beam model is a parameter of tire which is related to the transverse deflections and wear of tires. In the present study, the theoretical explanation of Gough stiffness was proposed to analyze the lateral bending deformation of the tire under different belt angles. By revising the Fiala tire model, the tire was simplified as composite beam on elastic foundation. The sidewall and tire tread pattern blocks were treated as an elastic foundation. The belt and tire body were simplified as a composite beam. Considering the high order shear deformation theory and the anisotropy of the cord-rubber material, the equilibrium equations were derived by using the principle of virtual work. The deformations under the transverse load with small deflections were derived for the first time. To verify the accuracy of the model, the theoretical results were compared with the results of finite element analysis, and the good agreement could be found. The effect of length, height, thickness and modulus of cord and rubber were analyzed. It is indicated that if the length-height ratio of the equivalent beam is unchanged, the corresponding belt angle of the maximum value of Gough stiffness will not be changed. According to maximum Gough stiffness, the optimal belt angle of the tire with different high width ratio was obtained. The results also agree with those results of the actual tire structure. The proposed model can provide theoretical direction for the structure and durability design of tires.
Tire is a kind of rubber-cord reinforced composite structure. Gough stiffness derived by using a beam model is a parameter of tire which is related to the transverse deflections and wear of tires. In the present study, the theoretical explanation of Gough stiffness was proposed to analyze the lateral bending deformation of the tire under different belt angles. By revising the Fiala tire model, the tire was simplified as composite beam on elastic foundation. The sidewall and tire tread pattern blocks were treated as an elastic foundation. The belt and tire body were simplified as a composite beam. Considering the high order shear deformation theory and the anisotropy of the cord-rubber material, the equilibrium equations were derived by using the principle of virtual work. The deformations under the transverse load with small deflections were derived for the first time. To verify the accuracy of the model, the theoretical results were compared with the results of finite element analysis, and the good agreement could be found. The effect of length, height, thickness and modulus of cord and rubber were analyzed. It is indicated that if the length-height ratio of the equivalent beam is unchanged, the corresponding belt angle of the maximum value of Gough stiffness will not be changed. According to maximum Gough stiffness, the optimal belt angle of the tire with different high width ratio was obtained. The results also agree with those results of the actual tire structure. The proposed model can provide theoretical direction for the structure and durability design of tires.
2019, 36(2): 533-543.
doi: 10.13801/j.cnki.fhclxb.20180411.001
Abstract:
In order to explore the relationship between the change of characteristic functional groups and the complex shear modulus of asphalt binder after repeated water-temperature cycles in seasonal frozen area, the SBS modified asphalts binders after 0, 3, 6, 9, 12, 15 and 18 times water-temperature cycles were tested by combing FTIR with dynamic shear rheological (DSR) testing techniques. The disciplinarian of complex shear modulus and the characteristic function groups of styrene-butadiene-styrene (SBS) modified asphalt binder under multiple water-temperature cycles were ascertained. Correlation between the complex shear modulus and the content of the characteristic functional groups was clarified based on the mathematical model of gray relational entropy analysis. Multivariate statistical regression analysis of the complex shear modulus G* of the SBS modified asphalt binder and the change functional group index by FTIR test under different temperatures and frequencies were conducted based on the Levenberg-Marquardt method and the generalized global optimization algorithm, and the prediction model of complex shear modulus of SBS modified asphalt binder was proposed. The results show that the asphalt binder has been aged after multiple water-temperature cycles, but SBS modifier has inhibitory effect on asphalt aging. The sulfoxide and carbonyl groups in the FTIR spectra of asphalt binder show an obviously increasing tendency with the increases of water-temperature cycles. The aliphatic is the highest of the six for SBS modified asphalt characteristic functional groups changes on the complex shear modulus impact, with the asymmetric aliphatic, aromatic compounds, styrene plus butadiene, sulfoxide and carbonyl following. The complex shear modulus of the SBS modified asphalt binder after multiple water-temperature cycles shows a multiple linear relationship with the change of characteristic functional groups.
In order to explore the relationship between the change of characteristic functional groups and the complex shear modulus of asphalt binder after repeated water-temperature cycles in seasonal frozen area, the SBS modified asphalts binders after 0, 3, 6, 9, 12, 15 and 18 times water-temperature cycles were tested by combing FTIR with dynamic shear rheological (DSR) testing techniques. The disciplinarian of complex shear modulus and the characteristic function groups of styrene-butadiene-styrene (SBS) modified asphalt binder under multiple water-temperature cycles were ascertained. Correlation between the complex shear modulus and the content of the characteristic functional groups was clarified based on the mathematical model of gray relational entropy analysis. Multivariate statistical regression analysis of the complex shear modulus G* of the SBS modified asphalt binder and the change functional group index by FTIR test under different temperatures and frequencies were conducted based on the Levenberg-Marquardt method and the generalized global optimization algorithm, and the prediction model of complex shear modulus of SBS modified asphalt binder was proposed. The results show that the asphalt binder has been aged after multiple water-temperature cycles, but SBS modifier has inhibitory effect on asphalt aging. The sulfoxide and carbonyl groups in the FTIR spectra of asphalt binder show an obviously increasing tendency with the increases of water-temperature cycles. The aliphatic is the highest of the six for SBS modified asphalt characteristic functional groups changes on the complex shear modulus impact, with the asymmetric aliphatic, aromatic compounds, styrene plus butadiene, sulfoxide and carbonyl following. The complex shear modulus of the SBS modified asphalt binder after multiple water-temperature cycles shows a multiple linear relationship with the change of characteristic functional groups.
