2018 Vol. 35, No. 4
2018, 35(4): 733-747.
doi: 10.13801/j.cnki.fhclxb.20171208.005
Abstract:
Fiber metal laminates (FMLs) has superior comprehensive mechanical properties, which leads to a successfully application in aerospace structures. High velocity impact property is one of the most important components for mechanical properties of FMLs. However, the related investigation for FMLs still in initial stage as the result from the complexity of failure mechanisms of high velocity impact. The mechanical properties of FMLs were discussed firstly. Then, the research status of FMLs' high velocity impact properties from experimental and numerical aspects was summarized. At last, the recommendations were proposed about existing problems and potential development trends in this area.
Fiber metal laminates (FMLs) has superior comprehensive mechanical properties, which leads to a successfully application in aerospace structures. High velocity impact property is one of the most important components for mechanical properties of FMLs. However, the related investigation for FMLs still in initial stage as the result from the complexity of failure mechanisms of high velocity impact. The mechanical properties of FMLs were discussed firstly. Then, the research status of FMLs' high velocity impact properties from experimental and numerical aspects was summarized. At last, the recommendations were proposed about existing problems and potential development trends in this area.
2018, 35(4): 748-759.
doi: 10.13801/j.cnki.fhclxb.20180329.001
Abstract:
The composites made from 3D woven preforms(3DWCs) have attracted far more attentions due to their very high specific-strength, low density, low thermal expansion and excellent formability, which have been successfully employed in aircraft and automobile engineering. With the research and development of aero engine are increasing, 3DWCs have also been applied to engine parts. The current research progress and current situation of 3D woven preforms(3DWPs)for the composite blades of aero engine were summarized; A contrastive analysis of several weaving methods of special-shaped high thickness 3DWPs was carried out; The research progress of deformation performance of 3DWPs was recommended based on experimentation and simulation; The effect of 3DWPs structure on the properties of the composites was also introduced; Furthermore, the challenges and outlook of the 3DWPs were outlined, thus it provided some reference gist for the deeper research on the development of composite blades of aero engine.
The composites made from 3D woven preforms(3DWCs) have attracted far more attentions due to their very high specific-strength, low density, low thermal expansion and excellent formability, which have been successfully employed in aircraft and automobile engineering. With the research and development of aero engine are increasing, 3DWCs have also been applied to engine parts. The current research progress and current situation of 3D woven preforms(3DWPs)for the composite blades of aero engine were summarized; A contrastive analysis of several weaving methods of special-shaped high thickness 3DWPs was carried out; The research progress of deformation performance of 3DWPs was recommended based on experimentation and simulation; The effect of 3DWPs structure on the properties of the composites was also introduced; Furthermore, the challenges and outlook of the 3DWPs were outlined, thus it provided some reference gist for the deeper research on the development of composite blades of aero engine.
2018, 35(4): 760-766.
doi: 10.13801/j.cnki.fhclxb.20170607.001
Abstract:
The demands of polymer-based composites with high thermal conductivity and low filler loading are significant in many applications such as electronic packaging and high-power electronic equipment. In general, the enhanced thermal conductivity requires dispersed filler with high loading in polymer matrix. However, the large amount of fillers usually results in the large degradation of mechanical property and high cost, which will lead to the composites difficult to meet the demands of present industrial applications. In this review, the current research progress on polymer-based composites with high thermal conductivity and low loading was discussed. Its thermal conduction mechanism and some factors, which primarily affected the thermal conductivity of composites, were recommended. And some methods that were used in preparing polymer-based composites with a thermal conductivity over 1.0 W/(m·K) and a low filler loading below 10vol%, were introduced according to different filler type. The challenges and outlook for polymer-based composites with high thermal conductivity and low filler loading were outlined.
The demands of polymer-based composites with high thermal conductivity and low filler loading are significant in many applications such as electronic packaging and high-power electronic equipment. In general, the enhanced thermal conductivity requires dispersed filler with high loading in polymer matrix. However, the large amount of fillers usually results in the large degradation of mechanical property and high cost, which will lead to the composites difficult to meet the demands of present industrial applications. In this review, the current research progress on polymer-based composites with high thermal conductivity and low loading was discussed. Its thermal conduction mechanism and some factors, which primarily affected the thermal conductivity of composites, were recommended. And some methods that were used in preparing polymer-based composites with a thermal conductivity over 1.0 W/(m·K) and a low filler loading below 10vol%, were introduced according to different filler type. The challenges and outlook for polymer-based composites with high thermal conductivity and low filler loading were outlined.
2018, 35(4): 767-773.
doi: 10.13801/j.cnki.fhclxb.20170704.001
Abstract:
The stiffness and strength of hybrid fiber reinforced polymer(HFRP) with plain fabric as reinforcement were studied. The hot-pressing process was designed and 7 groups of carbon-basalt hybrid fiber reinforced epoxy resin matrix composites specimens with different hybrid ratios were prepared for tensile test. Based on the structural characteristics of plain fabric, the traditional hybrid law was modified and a HFRP stiffness estimation model using plain fabric as reinforcement was proposed. According to the failure mechanism of HFRP laminates, the critical hybrid ratio of materials with only one failure was proposed and a strength estimation model with three ranges of hybrid ratios was also given. Finally, the estimation results were corrected by the coefficient of hybrid effect which reflects dispersion. The result shows that the calculated values and experimental values are similar and the critical hybrid ratio calculated fits the result of stress-strain curve analysis. The model can provide a theoretical basis for practical application in the future. The prediction method proposed in this paper can reflect the influence of hybrid ratio on the HFRP strength and stiffness of plain fabric, and expands the range of application of the mixture law.
The stiffness and strength of hybrid fiber reinforced polymer(HFRP) with plain fabric as reinforcement were studied. The hot-pressing process was designed and 7 groups of carbon-basalt hybrid fiber reinforced epoxy resin matrix composites specimens with different hybrid ratios were prepared for tensile test. Based on the structural characteristics of plain fabric, the traditional hybrid law was modified and a HFRP stiffness estimation model using plain fabric as reinforcement was proposed. According to the failure mechanism of HFRP laminates, the critical hybrid ratio of materials with only one failure was proposed and a strength estimation model with three ranges of hybrid ratios was also given. Finally, the estimation results were corrected by the coefficient of hybrid effect which reflects dispersion. The result shows that the calculated values and experimental values are similar and the critical hybrid ratio calculated fits the result of stress-strain curve analysis. The model can provide a theoretical basis for practical application in the future. The prediction method proposed in this paper can reflect the influence of hybrid ratio on the HFRP strength and stiffness of plain fabric, and expands the range of application of the mixture law.
2018, 35(4): 774-784.
doi: 10.13801/j.cnki.fhclxb.20170705.003
Abstract:
Graphene oxide (GO) was partially modified with ethylenediamine to obtain EGO, used as a modifier. Linear polyurethane containing silicone was firstly synthesized, using isophorone diisocyanate, polyether diol, hydroxyl silicone(HPMS) and dimethylol propionic acid as the main raw materials, then it was grafted onto the polyhydroxy hyperbranched polyurethane core(HBPU-0) from laboratory homemade, and finally it reacted with EGO to prepare ethanediamined GO/hyperbranched polyurethane containing silicone(EGO-HPMS/HBPU). The morphology and properties of the ethylenediamined GO-hydroxyl silicone/hyperbranched polyurethane composite emulsion and its films were characterized by FTIR, Raman, XRD, XPS, TEM, AFM, SEM and TG, and the effects of the contents of EGO and hydroxyl silicone oil on EGO-HPMS/HBPU composite properties were studied. The results show that EGO is stably dispersed in HBPU matrix when the amount of HPMS is 4wt% and EGO is 0.5wt%. Compared with the single modified material, the properties of the synergistic modified EGO-4wt%HPMS/HBPU composites are the best. The increase of the pyrolysis temperature under different mass loss displays the good stability of the material, and the 24 h water absorption reduces to 5.13%, and the water contact angle is 101.3°. The tensile strength and elongation at break of EGO-4wt%HPMS/HBPU are 11.18 MPa and 553.2%, respectively, to get hydrophobic and feeling smooth and soft composite products.
Graphene oxide (GO) was partially modified with ethylenediamine to obtain EGO, used as a modifier. Linear polyurethane containing silicone was firstly synthesized, using isophorone diisocyanate, polyether diol, hydroxyl silicone(HPMS) and dimethylol propionic acid as the main raw materials, then it was grafted onto the polyhydroxy hyperbranched polyurethane core(HBPU-0) from laboratory homemade, and finally it reacted with EGO to prepare ethanediamined GO/hyperbranched polyurethane containing silicone(EGO-HPMS/HBPU). The morphology and properties of the ethylenediamined GO-hydroxyl silicone/hyperbranched polyurethane composite emulsion and its films were characterized by FTIR, Raman, XRD, XPS, TEM, AFM, SEM and TG, and the effects of the contents of EGO and hydroxyl silicone oil on EGO-HPMS/HBPU composite properties were studied. The results show that EGO is stably dispersed in HBPU matrix when the amount of HPMS is 4wt% and EGO is 0.5wt%. Compared with the single modified material, the properties of the synergistic modified EGO-4wt%HPMS/HBPU composites are the best. The increase of the pyrolysis temperature under different mass loss displays the good stability of the material, and the 24 h water absorption reduces to 5.13%, and the water contact angle is 101.3°. The tensile strength and elongation at break of EGO-4wt%HPMS/HBPU are 11.18 MPa and 553.2%, respectively, to get hydrophobic and feeling smooth and soft composite products.
2018, 35(4): 785-792.
doi: 10.13801/j.cnki.fhclxb.20170705.004
Abstract:
SiO2-GO nanohybrid particle was produced via insitu hydrolysis. Through adding SiO2, GO, SiO2-GO nanohybrid particles and polyvinylpyrrolidone (PVP) respectively, the polyvinylidene fluoride(PVDF) hybrid membrane was first prepared through phase inversion by an immersion precipitation technique. The pure water flux, contact angle, fouling recover rate of PVDF hybrid membrane etc were determined. The results show that the contact angles of SiO2-GO/PVDF-PVP hybrid membrane decrease from 78.4° to 66.02°. The rejection rate of bovine serum albumin (BSA) exceeds 81.5% under high water flux (1 018 L/(m2·h)) and the membrane fouling recovery rate is highest (BSA=78.65%). The results show that the synergistic effect of SiO2-GO nanohybrid particles and PVP improve the properties and antifouling ability of hybrid membrane.
SiO2-GO nanohybrid particle was produced via insitu hydrolysis. Through adding SiO2, GO, SiO2-GO nanohybrid particles and polyvinylpyrrolidone (PVP) respectively, the polyvinylidene fluoride(PVDF) hybrid membrane was first prepared through phase inversion by an immersion precipitation technique. The pure water flux, contact angle, fouling recover rate of PVDF hybrid membrane etc were determined. The results show that the contact angles of SiO2-GO/PVDF-PVP hybrid membrane decrease from 78.4° to 66.02°. The rejection rate of bovine serum albumin (BSA) exceeds 81.5% under high water flux (1 018 L/(m2·h)) and the membrane fouling recovery rate is highest (BSA=78.65%). The results show that the synergistic effect of SiO2-GO nanohybrid particles and PVP improve the properties and antifouling ability of hybrid membrane.
2018, 35(4): 793-803.
doi: 10.13801/j.cnki.fhclxb.20170702.001
Abstract:
By using the classical lamination theory (CLT) and considering the coupling effect of tension and bending, an analytical model of stiffness prediction was developed for composite laminates with in-plane waviness. The influence of the parameters associated with in-plane waviness such as the waviness ration, the fiber off-axis angle and the waviness position on the 3D stiffness of the laminates was investigated quantitatively. It is found that the theoretical predictions agree well with the results in literature. And the longitudinal elastic modulus, the transverse elastic modulus, the in-plane shear modulus, the major Poisson's ratio, and the in-plane bending stiffness are greatly affected by the waviness defect. The approach established provides a procedure to evaluate the effects of waviness defect on the mechanical properties of composite laminates.
By using the classical lamination theory (CLT) and considering the coupling effect of tension and bending, an analytical model of stiffness prediction was developed for composite laminates with in-plane waviness. The influence of the parameters associated with in-plane waviness such as the waviness ration, the fiber off-axis angle and the waviness position on the 3D stiffness of the laminates was investigated quantitatively. It is found that the theoretical predictions agree well with the results in literature. And the longitudinal elastic modulus, the transverse elastic modulus, the in-plane shear modulus, the major Poisson's ratio, and the in-plane bending stiffness are greatly affected by the waviness defect. The approach established provides a procedure to evaluate the effects of waviness defect on the mechanical properties of composite laminates.
2018, 35(4): 804-814.
doi: 10.13801/j.cnki.fhclxb.20170609.002
Abstract:
Hemp fiber/polypropylene(HF/PP) composites were prepared via non-woven and compressing technology. The volatile organic compounds(VOC) emission source of HF/PP composites was studied and TG-mass spectrometry (TG-MS) was used to study the effect of PVA and urea modification on the VOC emission of HF/PP composites. At the same time the effect of the above methods on the mechanical and thermal properties of HF/PP composites were also investigated. The results reveal that the VOC emission of HF/PP composites mainly comes from hemp fiber. Compared with the untreated composite, the mechanical properties of the modified HF/PP composites are improved. The tensile strength and flexural strength of the composite reach the maximum value after urea modification which increase by 19.32% and 15.04% compared with untreated. The tensile modulus, flexural modulus and impact strength of the HF/PP composite reach the maximum value after PVA modification which increase by 17.72%, 15.94% and 24.72% compared with untreated. The thermal stability and VOC emission of the modified HF/PP composites are optimized after modification. The HF/PP composite attains the optimal thermal stability after PVA modification, and the total activation energy increases by 121.99% compared with untreated, and reaches to 392.56 kJ·mol-1. The thermal stability of HF/PP composites is closely related to its interfacial properties. The total VOC cumulative emission of the modified HF/PP composites decreases compared with untreated, and the urea modified composite exhibits the best effect.
Hemp fiber/polypropylene(HF/PP) composites were prepared via non-woven and compressing technology. The volatile organic compounds(VOC) emission source of HF/PP composites was studied and TG-mass spectrometry (TG-MS) was used to study the effect of PVA and urea modification on the VOC emission of HF/PP composites. At the same time the effect of the above methods on the mechanical and thermal properties of HF/PP composites were also investigated. The results reveal that the VOC emission of HF/PP composites mainly comes from hemp fiber. Compared with the untreated composite, the mechanical properties of the modified HF/PP composites are improved. The tensile strength and flexural strength of the composite reach the maximum value after urea modification which increase by 19.32% and 15.04% compared with untreated. The tensile modulus, flexural modulus and impact strength of the HF/PP composite reach the maximum value after PVA modification which increase by 17.72%, 15.94% and 24.72% compared with untreated. The thermal stability and VOC emission of the modified HF/PP composites are optimized after modification. The HF/PP composite attains the optimal thermal stability after PVA modification, and the total activation energy increases by 121.99% compared with untreated, and reaches to 392.56 kJ·mol-1. The thermal stability of HF/PP composites is closely related to its interfacial properties. The total VOC cumulative emission of the modified HF/PP composites decreases compared with untreated, and the urea modified composite exhibits the best effect.
2018, 35(4): 815-822.
doi: 10.13801/j.cnki.fhclxb.20170602.001
Abstract:
The effects of heat treatments on the crystallization behavior of polyamide 6 (PA6) on the surface of carbon fiber (CF) and their interfacial properties were explored. The effects of heat treatments on the crystallization behavior of PA6 on the surface of CF were characterized by differential scanning calorimetry (DSC) and polarizing microscope (POM) observation. The results show that the PA6 segments are rearranged during the heat treatment to form small and imperfect new crystals, which leads to the increase of crystallinity and the improvement of interfacial transcrystallization morphology. The interfacial property of CF/PA6 composites was characterized by micro-debonding test and unidirectional CF/PA6 composites transverse tensile test. It is revealed that the decrease of the weak interface and the stress concentration lead to the increase of the interfacial shear strength and the decrease of the fracture energy per unit volume of the annealed samples of CF/PA6 composites.
The effects of heat treatments on the crystallization behavior of polyamide 6 (PA6) on the surface of carbon fiber (CF) and their interfacial properties were explored. The effects of heat treatments on the crystallization behavior of PA6 on the surface of CF were characterized by differential scanning calorimetry (DSC) and polarizing microscope (POM) observation. The results show that the PA6 segments are rearranged during the heat treatment to form small and imperfect new crystals, which leads to the increase of crystallinity and the improvement of interfacial transcrystallization morphology. The interfacial property of CF/PA6 composites was characterized by micro-debonding test and unidirectional CF/PA6 composites transverse tensile test. It is revealed that the decrease of the weak interface and the stress concentration lead to the increase of the interfacial shear strength and the decrease of the fracture energy per unit volume of the annealed samples of CF/PA6 composites.
2018, 35(4): 823-833.
doi: 10.13801/j.cnki.fhclxb.20170720.001
Abstract:
The dynamic mechanics properties of 3D four directional braided carbon fiber reinforced resin matrix composites were investigated using split Hopkinson pressure bar(SHPB). Conducting experiments on specimens of different braid angles in longitudinal, transverse and thickness directions, the stress-strain curves of the composites were obtained at strain rate ranging from 800/s to 2 000/s, and the quasi-static compression test results were also included. The influence of strain rate, compressive direction and braid angle on ultimate strength and elastic modulus was discussed. And the processes of experiments were recorded by high-speed camera, thus the effect of strain rate and compressive direction on the failure mode can be further analyzed. The results show that the 3D four directional braided composite is sensitive to strain rate in all three compressive directions, with ultimate strength and elastic modulus both increasing as strain rate rises, and it becomes more fragile in high strain rate compared with quasi-static conditions. The braid angle has influence on dynamic compressive properties, which is the most when it comes to the longitudinal direction. The failure mode of the composite changes in different compressive directions and strain rates.
The dynamic mechanics properties of 3D four directional braided carbon fiber reinforced resin matrix composites were investigated using split Hopkinson pressure bar(SHPB). Conducting experiments on specimens of different braid angles in longitudinal, transverse and thickness directions, the stress-strain curves of the composites were obtained at strain rate ranging from 800/s to 2 000/s, and the quasi-static compression test results were also included. The influence of strain rate, compressive direction and braid angle on ultimate strength and elastic modulus was discussed. And the processes of experiments were recorded by high-speed camera, thus the effect of strain rate and compressive direction on the failure mode can be further analyzed. The results show that the 3D four directional braided composite is sensitive to strain rate in all three compressive directions, with ultimate strength and elastic modulus both increasing as strain rate rises, and it becomes more fragile in high strain rate compared with quasi-static conditions. The braid angle has influence on dynamic compressive properties, which is the most when it comes to the longitudinal direction. The failure mode of the composite changes in different compressive directions and strain rates.
2018, 35(4): 834-842.
doi: 10.13801/j.cnki.fhclxb.20170702.002
Abstract:
Three-dimensional FEM models were used to simulate the Z-pin/stitching reinforced T-joint specimens. The interface failure was simulated with cohesive zone model, and the effect of Z-pin/stitching was simulated with nonlinear springs inserted into the interface. The mechanical properties of the spring, i.e. bridging law, were obtained based on a micromechanical approach. Comparing with experimental results and the FEM results, it is difficult to increase the shear carrying capacity of T-joints through Z-pin/stitching as the shear carrying capacity of unreinforced T-joint is quite high already. After analyzing the a few schemes which can increase the shear carrying capacity of T-joints, choosing stitch with high tensile strength and low tensile modulus was suggested to be used for the design of interface reinforcement.
Three-dimensional FEM models were used to simulate the Z-pin/stitching reinforced T-joint specimens. The interface failure was simulated with cohesive zone model, and the effect of Z-pin/stitching was simulated with nonlinear springs inserted into the interface. The mechanical properties of the spring, i.e. bridging law, were obtained based on a micromechanical approach. Comparing with experimental results and the FEM results, it is difficult to increase the shear carrying capacity of T-joints through Z-pin/stitching as the shear carrying capacity of unreinforced T-joint is quite high already. After analyzing the a few schemes which can increase the shear carrying capacity of T-joints, choosing stitch with high tensile strength and low tensile modulus was suggested to be used for the design of interface reinforcement.
2018, 35(4): 843-849.
doi: 10.13801/j.cnki.fhclxb.20170704.002
Abstract:
The woven composite laminates with 2 mm in thickness were impacted by the hemispherical-nosed projectiles launched using a one-stage gas gun, and the impact angles were 0°, 30° and 45°. The process of projectiles impacting targets was recorded by a high-speed camera and the velocities of the projectiles were obtained. The experimental data was processed by the fitting formula to obtain the ballistic limit velocities at each impact angle and the results were compared with the theoretical model. The influence of the impact angles on the ballistic limits, energy absorption efficiency(EAE) and failure modes of the targets was analyzed. The results show that the ballistic limit of 45° oblique impact is the highest, then is normal impact and 30° impact is lowest. At the same impact energy, the energy absorption efficiency of 45° oblique impact is the highest, the EAE of 30° impact is more than normal impact at lower impact energy(<80 J), however, the EAE of normal impact is higher at higher energy(>80 J). The front surface of the targets is formed into circular indentation due to shear failure and the back is diamond bulge due to tensile fiber failure when impact normally. The targets are formed an ellipse reaming and their area increase with the increase of the impact velocity when oblique impact.
The woven composite laminates with 2 mm in thickness were impacted by the hemispherical-nosed projectiles launched using a one-stage gas gun, and the impact angles were 0°, 30° and 45°. The process of projectiles impacting targets was recorded by a high-speed camera and the velocities of the projectiles were obtained. The experimental data was processed by the fitting formula to obtain the ballistic limit velocities at each impact angle and the results were compared with the theoretical model. The influence of the impact angles on the ballistic limits, energy absorption efficiency(EAE) and failure modes of the targets was analyzed. The results show that the ballistic limit of 45° oblique impact is the highest, then is normal impact and 30° impact is lowest. At the same impact energy, the energy absorption efficiency of 45° oblique impact is the highest, the EAE of 30° impact is more than normal impact at lower impact energy(<80 J), however, the EAE of normal impact is higher at higher energy(>80 J). The front surface of the targets is formed into circular indentation due to shear failure and the back is diamond bulge due to tensile fiber failure when impact normally. The targets are formed an ellipse reaming and their area increase with the increase of the impact velocity when oblique impact.
2018, 35(4): 850-856.
doi: 10.13801/j.cnki.fhclxb.20170620.003
Abstract:
According to thermal insulation mechanism of vacuum insulation panels (VIP), service life evaluation model of VIP was established and service life of VIP with glass fiber core materials was predicted by the model. Accelerated aging model of VIP was proposed based on Arrhenius law, these parameters of which were determined by aging experiments. In addition, the activation energy of VIP was also obtained. The service life of VIP at different temperatures can be predicted by accelerated aging model. The reliability of two models was verified by the tracking test results of test sample. The methods of improving the thermal insulation performance and prolonging the service life of VIP were discussed. The scientific research work in this paper provides theoretical basis and technical support to optimize key technology and process parameters of VIP.
According to thermal insulation mechanism of vacuum insulation panels (VIP), service life evaluation model of VIP was established and service life of VIP with glass fiber core materials was predicted by the model. Accelerated aging model of VIP was proposed based on Arrhenius law, these parameters of which were determined by aging experiments. In addition, the activation energy of VIP was also obtained. The service life of VIP at different temperatures can be predicted by accelerated aging model. The reliability of two models was verified by the tracking test results of test sample. The methods of improving the thermal insulation performance and prolonging the service life of VIP were discussed. The scientific research work in this paper provides theoretical basis and technical support to optimize key technology and process parameters of VIP.
2018, 35(4): 857-865.
doi: 10.13801/j.cnki.fhclxb.20170621.001
Abstract:
A design and analysis method of multifunctional composite laminates, merging bistable characteristics and antenna function was presented. Based on nonlinear laminated theory and Rayleigh-Ritz method, the stable geometrical configuration of the bistable hybrid laminate was predicted. The theoretical, finite element analysis and measured stable geometrical configurations agree well with each other. The critical loads and electromagnetic performance of the bistable hybrid laminate were investigated. The influences of lay-ups on the configurations, critical loads and electromagnetic performance of the bistable laminate were studied. The results indicate that the main direction of the antenna is reconfigured about 30° in the vertical plane which can expand the beam steering by changing the two stable state of the hybrid laminate. The lay-ups of the laminate has a great influence on the configurations and reflection coefficient of bistable laminate. When the polyimide film thickness is higher than 0.2 mm, the laminate with surface antenna radiation layer has no bistable characteristics and its center frequency will shift to left about 0.2 GHz.
A design and analysis method of multifunctional composite laminates, merging bistable characteristics and antenna function was presented. Based on nonlinear laminated theory and Rayleigh-Ritz method, the stable geometrical configuration of the bistable hybrid laminate was predicted. The theoretical, finite element analysis and measured stable geometrical configurations agree well with each other. The critical loads and electromagnetic performance of the bistable hybrid laminate were investigated. The influences of lay-ups on the configurations, critical loads and electromagnetic performance of the bistable laminate were studied. The results indicate that the main direction of the antenna is reconfigured about 30° in the vertical plane which can expand the beam steering by changing the two stable state of the hybrid laminate. The lay-ups of the laminate has a great influence on the configurations and reflection coefficient of bistable laminate. When the polyimide film thickness is higher than 0.2 mm, the laminate with surface antenna radiation layer has no bistable characteristics and its center frequency will shift to left about 0.2 GHz.
2018, 35(4): 866-875.
doi: 10.13801/j.cnki.fhclxb.20170705.001
Abstract:
There are some special issues in manufacturing, modeling and layup optimization for maximum buckling load of variable-stiffness composite laminates compared with traditional ones. Firstly, the manufacturing factors which need to be considered when designing variable-stiffness laminates were summarized and the design requirements for buckling were proposed. Secondly, two modelling methods were developed, namely the ideal model and the model considering the tow width. An automatic parametric modeling program was written based on the secondary development of ABAQUS. Buckling analysis was carried on a series of variable-stiffness plates with different ply angles, and the restriction of the minimum curvature radius was discussed and the reasons for the increase in the buckling performance of variable-stiffness laminates were explained. Based on the mechanism of increasing buckling load, a layup optimization method to maximize the buckling load of variable-stiffness laminates was created and the optimum layup was obtained using a two-step genetic algorithm. Finally, the tow width and ply staggering effects on the layup optimization for maximum buckling load were investigated using the model considering the tow width. The result demonstrates that it is generally feasible to apply the simplified ideal model when carrying out the layup optimization for maximum buckling load of variable-stiffness laminates. Considering the manufacturing factors, the optimum variable-stiffness plate increases the buckling load dramatically compared with the traditional one.
There are some special issues in manufacturing, modeling and layup optimization for maximum buckling load of variable-stiffness composite laminates compared with traditional ones. Firstly, the manufacturing factors which need to be considered when designing variable-stiffness laminates were summarized and the design requirements for buckling were proposed. Secondly, two modelling methods were developed, namely the ideal model and the model considering the tow width. An automatic parametric modeling program was written based on the secondary development of ABAQUS. Buckling analysis was carried on a series of variable-stiffness plates with different ply angles, and the restriction of the minimum curvature radius was discussed and the reasons for the increase in the buckling performance of variable-stiffness laminates were explained. Based on the mechanism of increasing buckling load, a layup optimization method to maximize the buckling load of variable-stiffness laminates was created and the optimum layup was obtained using a two-step genetic algorithm. Finally, the tow width and ply staggering effects on the layup optimization for maximum buckling load were investigated using the model considering the tow width. The result demonstrates that it is generally feasible to apply the simplified ideal model when carrying out the layup optimization for maximum buckling load of variable-stiffness laminates. Considering the manufacturing factors, the optimum variable-stiffness plate increases the buckling load dramatically compared with the traditional one.
2018, 35(4): 876-884.
doi: 10.13801/j.cnki.fhclxb.20170628.001
Abstract:
Bamboo fiber extraction process was optimized by response surface design (Box-Behnken).The bamboo was boiled with alkali and JFC penetrant, and the bamboo fiber was extracted by mechanical rolling. The concentration of alkali was 0.5%-0.7%, the concentration of JFC was 0.1%-0.3% and the boiling time was 1.5-2.5 h, which were taken as the factors. The response surface method was used to establish the mathematical model to obtain the best performance of the bamboo fiber with the breaking strength, extraction rate, diameter and friction coefficient of bamboo fiber. The longitudinal structure of the bamboo fibers treated with different processes was observed by scanning electron microscopy. The results reveal that the optimal extraction process is 0.7% alkali, 0.3% JFC and 2.5 h boiling time. The optimum tensile strength is 386.25 MPa, the diameter is 191.79 μm and the friction coefficient is 0.206, which is close to the response surface prediction as tensile strength is 405.08 MPa, diameter is 175.59 μm and friction coefficient is 0.191.The performance of bamboo fiber optimized by response surface method is better, and the response surface can predict the test result well. The breaking strength differs from the predicted value by 4.6%, the friction coefficient differs from the predicted value by 7.8%, and the difference between the diameter and the predicted value is 9.2%. SEM reveals that the alkali treatment, JFC treatment and boiling time have an effect on the gum of the fiber. Alkali concentration of 0.5%, JFC concentration of 0.3% and boiling time of 2.5 h are conducive to the removal of bamboo fiber surface glial.
Bamboo fiber extraction process was optimized by response surface design (Box-Behnken).The bamboo was boiled with alkali and JFC penetrant, and the bamboo fiber was extracted by mechanical rolling. The concentration of alkali was 0.5%-0.7%, the concentration of JFC was 0.1%-0.3% and the boiling time was 1.5-2.5 h, which were taken as the factors. The response surface method was used to establish the mathematical model to obtain the best performance of the bamboo fiber with the breaking strength, extraction rate, diameter and friction coefficient of bamboo fiber. The longitudinal structure of the bamboo fibers treated with different processes was observed by scanning electron microscopy. The results reveal that the optimal extraction process is 0.7% alkali, 0.3% JFC and 2.5 h boiling time. The optimum tensile strength is 386.25 MPa, the diameter is 191.79 μm and the friction coefficient is 0.206, which is close to the response surface prediction as tensile strength is 405.08 MPa, diameter is 175.59 μm and friction coefficient is 0.191.The performance of bamboo fiber optimized by response surface method is better, and the response surface can predict the test result well. The breaking strength differs from the predicted value by 4.6%, the friction coefficient differs from the predicted value by 7.8%, and the difference between the diameter and the predicted value is 9.2%. SEM reveals that the alkali treatment, JFC treatment and boiling time have an effect on the gum of the fiber. Alkali concentration of 0.5%, JFC concentration of 0.3% and boiling time of 2.5 h are conducive to the removal of bamboo fiber surface glial.
2018, 35(4): 885-895.
doi: 10.13801/j.cnki.fhclxb.20170628.002
Abstract:
Composite honeycomb plate is a class of important structure in the aerospace field. But it is rarely reported about the research on the modal characteristics of honeycomb structure in thermal environment. In this paper, modal tests on a plate composed by CF/epoxy laminates and Nomex honeycomb core were performed in six different temperature environments. During heating, the face sheet is debonded from the honeycomb core. Before delamination, natural frequencies of the plate decrease with the rising temperature. Among the first 7 modes, the decrease of the frequencies of bending modes is larger than that of the torsion modes. After debonding, the modal parameters of the plate at room temperature are quite different from the original structure. The modal damping ratio is significantly increased, and the order of two mode shapes is reversed. Lastly, the causes of the debonding of face sheet are analyzed and the conclusion is helpful to the structural design of composite honeycomb structures used in thermal environment.
Composite honeycomb plate is a class of important structure in the aerospace field. But it is rarely reported about the research on the modal characteristics of honeycomb structure in thermal environment. In this paper, modal tests on a plate composed by CF/epoxy laminates and Nomex honeycomb core were performed in six different temperature environments. During heating, the face sheet is debonded from the honeycomb core. Before delamination, natural frequencies of the plate decrease with the rising temperature. Among the first 7 modes, the decrease of the frequencies of bending modes is larger than that of the torsion modes. After debonding, the modal parameters of the plate at room temperature are quite different from the original structure. The modal damping ratio is significantly increased, and the order of two mode shapes is reversed. Lastly, the causes of the debonding of face sheet are analyzed and the conclusion is helpful to the structural design of composite honeycomb structures used in thermal environment.
2018, 35(4): 896-902.
doi: 10.13801/j.cnki.fhclxb.20170825.003
Abstract:
The (SiCP/Cu)-copper foil laminated composite materials were fabricated by dip coating and hot pressed sintering. The effects of SiCP content on the microstructure, tensil strength and fracture toughness of the (SiCP/Cu)-copper foil laminated composites were studied. The results show that the layer thickness of the (SiCP/Cu)-copper foil laminated composites is homogeneous, the interface bonding is in good condition, and the reinforced phase SiC disperses in the binding phase and interface. With the addition of SiCP, the tensile strength and yield strength firstly increase, and then decrease. When the volume fraction of SiCP is 20vol% (the total content is 100), the tensile strength and yield strength reach the maximum value of 226.5 MPa and 113.1 MPa, respectively. The fractural surface of the specimen after tensile strength test exhibits a ductile fracture mode in conjunction with some cleavage fracture features. The fracture toughness which the crack grow parallel to the layer interface has a little decrease with the increase of SiCP content, the (SiCP/Cu)-copper foil laminated composites with 15vol% SiCP content has maximum fracture toughness of 16.96 MPa·m1/2. When the crack grow perpendicular to the layer interface, the fracture toughness of the samples is also decreased with the increase of SiCP content, the (SiCP/Cu)-copper foil laminated composites with 15vol% SiCP reaches maximum fracture toughness of 12.51 MPa·m1/2.
The (SiCP/Cu)-copper foil laminated composite materials were fabricated by dip coating and hot pressed sintering. The effects of SiCP content on the microstructure, tensil strength and fracture toughness of the (SiCP/Cu)-copper foil laminated composites were studied. The results show that the layer thickness of the (SiCP/Cu)-copper foil laminated composites is homogeneous, the interface bonding is in good condition, and the reinforced phase SiC disperses in the binding phase and interface. With the addition of SiCP, the tensile strength and yield strength firstly increase, and then decrease. When the volume fraction of SiCP is 20vol% (the total content is 100), the tensile strength and yield strength reach the maximum value of 226.5 MPa and 113.1 MPa, respectively. The fractural surface of the specimen after tensile strength test exhibits a ductile fracture mode in conjunction with some cleavage fracture features. The fracture toughness which the crack grow parallel to the layer interface has a little decrease with the increase of SiCP content, the (SiCP/Cu)-copper foil laminated composites with 15vol% SiCP content has maximum fracture toughness of 16.96 MPa·m1/2. When the crack grow perpendicular to the layer interface, the fracture toughness of the samples is also decreased with the increase of SiCP content, the (SiCP/Cu)-copper foil laminated composites with 15vol% SiCP reaches maximum fracture toughness of 12.51 MPa·m1/2.
2018, 35(4): 903-909.
doi: 10.13801/j.cnki.fhclxb.20170609.003
Abstract:
MgO coated CoFe2O4 nanoparticles (CoFe2O4@MgO) were synthesized by the thermal decomposition of a metal-organic salt. CoFe2O4@MgO was reduced in H2 and then oxidized in air to prepare a group of CoFe2@CoFe2O4@MgO samples. Then MgO was dissolved by the HCl solution to obtain the other group of samples (CoFe2@CoF2O4). The magnetic field and temperature dependent magnetization curves were measured on CoFe2@CoF2O4 and CoFe2@CoFe2O4@MgO samples. The significant changes of coercivity Hc, saturation magnetization Ms and remanence ratio Mr/Ms as well as the magnetic ordering states with the oxidation temperature are observed for CoFe2@CoF2O4 and CoFe2@CoFe2O4@MgO samples, which strongly depend on the anisotropy of the magnetic particles and interparticle dipolar interaction.
MgO coated CoFe2O4 nanoparticles (CoFe2O4@MgO) were synthesized by the thermal decomposition of a metal-organic salt. CoFe2O4@MgO was reduced in H2 and then oxidized in air to prepare a group of CoFe2@CoFe2O4@MgO samples. Then MgO was dissolved by the HCl solution to obtain the other group of samples (CoFe2@CoF2O4). The magnetic field and temperature dependent magnetization curves were measured on CoFe2@CoF2O4 and CoFe2@CoFe2O4@MgO samples. The significant changes of coercivity Hc, saturation magnetization Ms and remanence ratio Mr/Ms as well as the magnetic ordering states with the oxidation temperature are observed for CoFe2@CoF2O4 and CoFe2@CoFe2O4@MgO samples, which strongly depend on the anisotropy of the magnetic particles and interparticle dipolar interaction.
2018, 35(4): 910-919.
doi: 10.13801/j.cnki.fhclxb.20170612.002
Abstract:
The 63vol% Diamond/Cu-Ti composites were prepared by vacuum hot pressing. The influence of minor Ti addition on the interfacial microstructure and thermal conductivity of Diamond/Cu-Ti composites was studied. The thermal conductivity of Diamond/Cu-Ti composites first increases and then decreases with increasing Ti contents. The maximum value of 511 W/(m·K) is obtained at 1.1wt%Ti. When Ti contents are less than 1.1wt%, the number and area of carbides generated during the sintering process increase with the increase of Ti content, the interface bonding is optimized, the interface bonding strength is improved, the number of interface heat transfer channels is increased and the thermal conductivity of Diamond/Cu-Ti composites is improved. The increase of Ti content is accompanied by the increase of carbide thermal resistance and the deterioration of the thermal conductivity of the matrix. The excess Ti element increases the thickness of the carbide layer with low thermal conductivity, increases the thermal resistance of the carbide layer itself, reduces the interfacial thermal conductivity, and decreases the thermal conductivity of the Diamond/Cu-Ti composites.
The 63vol% Diamond/Cu-Ti composites were prepared by vacuum hot pressing. The influence of minor Ti addition on the interfacial microstructure and thermal conductivity of Diamond/Cu-Ti composites was studied. The thermal conductivity of Diamond/Cu-Ti composites first increases and then decreases with increasing Ti contents. The maximum value of 511 W/(m·K) is obtained at 1.1wt%Ti. When Ti contents are less than 1.1wt%, the number and area of carbides generated during the sintering process increase with the increase of Ti content, the interface bonding is optimized, the interface bonding strength is improved, the number of interface heat transfer channels is increased and the thermal conductivity of Diamond/Cu-Ti composites is improved. The increase of Ti content is accompanied by the increase of carbide thermal resistance and the deterioration of the thermal conductivity of the matrix. The excess Ti element increases the thickness of the carbide layer with low thermal conductivity, increases the thermal resistance of the carbide layer itself, reduces the interfacial thermal conductivity, and decreases the thermal conductivity of the Diamond/Cu-Ti composites.
2018, 35(4): 920-926.
doi: 10.13801/j.cnki.fhclxb.20170614.001
Abstract:
Cu was coated on the surface of the nature graphite flake (GF) by the electroless copper plating method, and then the Cu-GF/Al composites were fabricated by vacuum hot-press sintering with Cu-coated GF (Cu-GF) and Al powder. The microstructures and interfaces of Cu-GF/Al composites were studied and the effect of Cu-GF surface on the thermal conductivity and bending strength was investigated. The results show that the Cu layer inhibits the formation of Al4C3. Thus the bending strength of Cu-GF/Al composites is significantly enhanced after Cu coated and the value decreases from 104 to 74 MPa as Cu-GF volume fraction increases from 50% to 70%. The maximum thermal conductivity is 522 W/(m·K) when the volume fraction of GF is 70%.
Cu was coated on the surface of the nature graphite flake (GF) by the electroless copper plating method, and then the Cu-GF/Al composites were fabricated by vacuum hot-press sintering with Cu-coated GF (Cu-GF) and Al powder. The microstructures and interfaces of Cu-GF/Al composites were studied and the effect of Cu-GF surface on the thermal conductivity and bending strength was investigated. The results show that the Cu layer inhibits the formation of Al4C3. Thus the bending strength of Cu-GF/Al composites is significantly enhanced after Cu coated and the value decreases from 104 to 74 MPa as Cu-GF volume fraction increases from 50% to 70%. The maximum thermal conductivity is 522 W/(m·K) when the volume fraction of GF is 70%.
2018, 35(4): 927-935.
doi: 10.13801/j.cnki.fhclxb.20170808.004
Abstract:
A constitutive model of particulate reinforced composites (PRCs) which can describe the evolution of debonding damage, matrix plasticity and particle size effects on deformation and damage was developed. An incremental damage model of PRC based on Mori-Tanaka's mean field concept had been extended to three-phase composites for interpreting particle size effect. The interphase was perfectly incorporated into the present micromechanics model as a third phase with the help of double-inclusion model. Progressive damage was controlled by a critical energy criterion for particle-matrix interfacial separation. Based on the developed model, the influences of progressive debonding damage, particle size and interphase properties on the overall stress-strain response of PRC were discussed. Finally, the particle size effect on the mechanical behaviors of composites was clearly interpreted from the role of the interphase, which was different from all the existing researches.
A constitutive model of particulate reinforced composites (PRCs) which can describe the evolution of debonding damage, matrix plasticity and particle size effects on deformation and damage was developed. An incremental damage model of PRC based on Mori-Tanaka's mean field concept had been extended to three-phase composites for interpreting particle size effect. The interphase was perfectly incorporated into the present micromechanics model as a third phase with the help of double-inclusion model. Progressive damage was controlled by a critical energy criterion for particle-matrix interfacial separation. Based on the developed model, the influences of progressive debonding damage, particle size and interphase properties on the overall stress-strain response of PRC were discussed. Finally, the particle size effect on the mechanical behaviors of composites was clearly interpreted from the role of the interphase, which was different from all the existing researches.
2018, 35(4): 936-945.
doi: 10.13801/j.cnki.fhclxb.20170705.002
Abstract:
A thermal modal analysis method was established by considering the effects of material property's change, thermal stress and deformation to investigate thermal modal evolution of composite stiffened and connecting plates. The calculation results show that material property's change and thermal stress result in the increasing in modal frequencies under thermal buckling temperature. In post-buckling stage, the nonlinear deformation can increase the stiffness of panel structures, which makes the modal frequencies increase. Mode changes occur during the whole warming-up process and modals tend to be dense; Initial deflections, size of stiffeners and reinforcement patterns have great influence on the critical buckling temperature of stiffened plates. Mode shapes are also changed and appear characteristics of localized. For connecting plates, due to the similarity of thermal deformation and modal shape, the modal frequency will jump from the lower order to the higher.
A thermal modal analysis method was established by considering the effects of material property's change, thermal stress and deformation to investigate thermal modal evolution of composite stiffened and connecting plates. The calculation results show that material property's change and thermal stress result in the increasing in modal frequencies under thermal buckling temperature. In post-buckling stage, the nonlinear deformation can increase the stiffness of panel structures, which makes the modal frequencies increase. Mode changes occur during the whole warming-up process and modals tend to be dense; Initial deflections, size of stiffeners and reinforcement patterns have great influence on the critical buckling temperature of stiffened plates. Mode shapes are also changed and appear characteristics of localized. For connecting plates, due to the similarity of thermal deformation and modal shape, the modal frequency will jump from the lower order to the higher.
2018, 35(4): 946-956.
doi: 10.13801/j.cnki.fhclxb.20170714.001
Abstract:
By means of coprecipitation, the precursor Ni0.8Co0.15Al0.05(CO3)x (OH)y with about 10 μm particle size was prepared. The cathode material of lithium ion battery, LiNi0.8Co0.15Al0.05O2 (LiNCA) was fabricated successfully with the precursor and LiOH·H2O, and the effects of calcination atmosphere, calcination temperature and calcination method on electrochemical performances were studied. The results show that the discharge specific capacity of the LiNCA calcined in oxygen reaches 170 mAh·g-1, and the capacity retention ratio after 50 cycles reaches 95%, which is better than the LiNCA calcined in air. In the oxygen atmosphere, the LiNCA obtains the best performance when the calcination temperature is in range of 700 to 750℃. If the calcination temperature is too high or too low, the performance of LiNCA decreases significantly. When the precursor is precalcined at 450℃ in oxygen atmosphere, and then calcined with mixed LiOH·H2O at 700 to 750℃, the LiNCA discharge specific capacity reaches 190 mAh·g-1, which increases significantly.
By means of coprecipitation, the precursor Ni0.8Co0.15Al0.05(CO3)x (OH)y with about 10 μm particle size was prepared. The cathode material of lithium ion battery, LiNi0.8Co0.15Al0.05O2 (LiNCA) was fabricated successfully with the precursor and LiOH·H2O, and the effects of calcination atmosphere, calcination temperature and calcination method on electrochemical performances were studied. The results show that the discharge specific capacity of the LiNCA calcined in oxygen reaches 170 mAh·g-1, and the capacity retention ratio after 50 cycles reaches 95%, which is better than the LiNCA calcined in air. In the oxygen atmosphere, the LiNCA obtains the best performance when the calcination temperature is in range of 700 to 750℃. If the calcination temperature is too high or too low, the performance of LiNCA decreases significantly. When the precursor is precalcined at 450℃ in oxygen atmosphere, and then calcined with mixed LiOH·H2O at 700 to 750℃, the LiNCA discharge specific capacity reaches 190 mAh·g-1, which increases significantly.
2018, 35(4): 957-963.
doi: 10.13801/j.cnki.fhclxb.20170622.001
Abstract:
Nickel nanowires were obtained using the porous alumina template by the alternating current electro-deposition method. For the first time, the Ni nanowire/cement composites were fabricated by using the as-obtained nanowires as the conductive filler, and the polycarboxylate superplasticizer as the dispersant. The microstructures of Ni nanowires and Ni nanowires/cement composites were studied by SEM, TEM and XRD. Besides, the percolation threshold and piezoresistivity of Ni nanowires/cement composites were investigated by the four-pole method. The results indicate that the diameter of as-obtained Ni nanowires is about 65 nm and the aspect ratio is about 50. Also, the polycarboxylate superplasticizer can effectively improve the dispersion of Ni nanowires. In addition, the resistivity of cement-based composites displays the typical features of percolation phenomena with the increase of Ni nanowires content, the percolation threshold is concluded to be 0.5vol%. Furthermore, the measured gage factor of Ni nanowires/cement composites with 1.0vol% Ni nanowires is 509.2, far higher than the value of 2.0 for the resistance-strain gauge. The Ni nanowires/cement composites are promising for the application as the stress sensor in the concrete structures.
Nickel nanowires were obtained using the porous alumina template by the alternating current electro-deposition method. For the first time, the Ni nanowire/cement composites were fabricated by using the as-obtained nanowires as the conductive filler, and the polycarboxylate superplasticizer as the dispersant. The microstructures of Ni nanowires and Ni nanowires/cement composites were studied by SEM, TEM and XRD. Besides, the percolation threshold and piezoresistivity of Ni nanowires/cement composites were investigated by the four-pole method. The results indicate that the diameter of as-obtained Ni nanowires is about 65 nm and the aspect ratio is about 50. Also, the polycarboxylate superplasticizer can effectively improve the dispersion of Ni nanowires. In addition, the resistivity of cement-based composites displays the typical features of percolation phenomena with the increase of Ni nanowires content, the percolation threshold is concluded to be 0.5vol%. Furthermore, the measured gage factor of Ni nanowires/cement composites with 1.0vol% Ni nanowires is 509.2, far higher than the value of 2.0 for the resistance-strain gauge. The Ni nanowires/cement composites are promising for the application as the stress sensor in the concrete structures.
2018, 35(4): 964-972.
doi: 10.13801/j.cnki.fhclxb.20170609.004
Abstract:
The effect of cellulose nanocrystals (CNC) addition on the properties of chitosan/polyvinyl alcohol (CS-PVA) matrix was explored, and the theoretical support for the fabrication of electrospun CNC/CS-PVA composite nanofibers was further provided. Using CNC, CS and PVA as raw materials, the CNC/CS-PVA composite nanofibers with different CNC content (mass fraction) were successfully prepared by the method of electrospinning. The microstructure and properties of the composite nanofibers were analyzed by SEM, TGA and FTIR. The results show that the addition of CNC leads to increased average diameter of the CNC/CS-PVA composite nanofibers, while the composite nanofibers surface becomes rougher. The mechanical properties and thermal behavior are significantly improved. With the increase of CNC content, the Young's modulus (E) and tensile strength (σ) of CNC/CS-PVA composite nanofibers first enhance and then weaken, while the epitaxial starting temperature continues to rise. When the content of CNC is 3wt%, the mechanical properties of electrospun CNC/CS-PVA composite nanofibers have the maximum values. Compared with CS-PVA composite nanofibers, E and σ of the nanofibers with CNC incorporation increase by 43.9% and 24.8%, respectively. As CNC content is 20wt%, the electrospun CNC/CS-PVA composite nanofibers diameter distribution is not uniform, some spherical structure is observed on the surface of the single fiber, and the epitaxial initiation temperature reaches to 328.83℃. FTIR analysis showes that only physical interaction is present among CNC, CS and PVA, but no chemical reaction occurres. The stability of the electrospun CNC/CS-PVA composite nanofibers with different CNC contents gradually increases with increased acidity of the solution, while the CNC loading has little effect on it.
The effect of cellulose nanocrystals (CNC) addition on the properties of chitosan/polyvinyl alcohol (CS-PVA) matrix was explored, and the theoretical support for the fabrication of electrospun CNC/CS-PVA composite nanofibers was further provided. Using CNC, CS and PVA as raw materials, the CNC/CS-PVA composite nanofibers with different CNC content (mass fraction) were successfully prepared by the method of electrospinning. The microstructure and properties of the composite nanofibers were analyzed by SEM, TGA and FTIR. The results show that the addition of CNC leads to increased average diameter of the CNC/CS-PVA composite nanofibers, while the composite nanofibers surface becomes rougher. The mechanical properties and thermal behavior are significantly improved. With the increase of CNC content, the Young's modulus (E) and tensile strength (σ) of CNC/CS-PVA composite nanofibers first enhance and then weaken, while the epitaxial starting temperature continues to rise. When the content of CNC is 3wt%, the mechanical properties of electrospun CNC/CS-PVA composite nanofibers have the maximum values. Compared with CS-PVA composite nanofibers, E and σ of the nanofibers with CNC incorporation increase by 43.9% and 24.8%, respectively. As CNC content is 20wt%, the electrospun CNC/CS-PVA composite nanofibers diameter distribution is not uniform, some spherical structure is observed on the surface of the single fiber, and the epitaxial initiation temperature reaches to 328.83℃. FTIR analysis showes that only physical interaction is present among CNC, CS and PVA, but no chemical reaction occurres. The stability of the electrospun CNC/CS-PVA composite nanofibers with different CNC contents gradually increases with increased acidity of the solution, while the CNC loading has little effect on it.
2018, 35(4): 973-979.
doi: 10.13801/j.cnki.fhclxb.20170622.002
Abstract:
Currently, the use of latex for conventional cementing shows a series of problems such as low salt resistance, poor freeze-thaw stability, bad toughening ability and poor integrated performance. In view of the above-mentioned facts styrene(St) as hard monomer and polybutadiene latex (PB) as seed soft monomer combine new type of functional monomer, were used to synthesize the latex HTL-100L by emulsion grafting polymerization method, which had the properties of heat resistance, salt tolerance, good freeze-thaw resistance and strong toughening ability. Microstructural analysis suggests that all monmers are participated in the reaction and and the HTL-100L is the target product. The molecular structure is stable at high temperature about 420℃. The performance test of HTL-100L portland cement matrix composites shows that HTL-100L significantly improves the toughness of pure cement whose elastic modulus decreases nearly 100% and the strength of portland cement stone developes well. it has the advantages of wide applicable temperature range(80-180℃), easily controlled system and good integrated performance. Thus, it can be applied to solve the problems in latex for conventional cementing and improve the comprehensive performance of oil well cement matrix composites.
Currently, the use of latex for conventional cementing shows a series of problems such as low salt resistance, poor freeze-thaw stability, bad toughening ability and poor integrated performance. In view of the above-mentioned facts styrene(St) as hard monomer and polybutadiene latex (PB) as seed soft monomer combine new type of functional monomer, were used to synthesize the latex HTL-100L by emulsion grafting polymerization method, which had the properties of heat resistance, salt tolerance, good freeze-thaw resistance and strong toughening ability. Microstructural analysis suggests that all monmers are participated in the reaction and and the HTL-100L is the target product. The molecular structure is stable at high temperature about 420℃. The performance test of HTL-100L portland cement matrix composites shows that HTL-100L significantly improves the toughness of pure cement whose elastic modulus decreases nearly 100% and the strength of portland cement stone developes well. it has the advantages of wide applicable temperature range(80-180℃), easily controlled system and good integrated performance. Thus, it can be applied to solve the problems in latex for conventional cementing and improve the comprehensive performance of oil well cement matrix composites.
2018, 35(4): 980-988.
doi: 10.13801/j.cnki.fhclxb.20171201.001
Abstract:
For increasing the dosage of paraffin in phase change cementitious composites, the pore forming agent (PFA) was mixed with phase change cementitious composites, in which a part of paraffin was filled into the pores produced by the PFA. The effects of different dosages of paraffin and PFA on the paraffin leakage, mechanical properties and thermal storage performance of phase change cementitious composites were studied. The results show that the dosage of paraffin in the phase change cementitious composites increases from 5.0% to 7.2% and the compressive strength decreases sharply with the content of PFA increasing from 0% to 4%. The optimum dosages of PFA and paraffin are 2% and 5.8%, respectively. The heat storage performance of phase change cementitious composites is enhanced with the increase of paraffin content. In addition, the thermal insulation effect of pores also contributes to the increase of the maximum temperature difference between the outer and inner wall of phase change cementitious composites plate and the decrease of the maximum temperature of the cavity in the measurement system.
For increasing the dosage of paraffin in phase change cementitious composites, the pore forming agent (PFA) was mixed with phase change cementitious composites, in which a part of paraffin was filled into the pores produced by the PFA. The effects of different dosages of paraffin and PFA on the paraffin leakage, mechanical properties and thermal storage performance of phase change cementitious composites were studied. The results show that the dosage of paraffin in the phase change cementitious composites increases from 5.0% to 7.2% and the compressive strength decreases sharply with the content of PFA increasing from 0% to 4%. The optimum dosages of PFA and paraffin are 2% and 5.8%, respectively. The heat storage performance of phase change cementitious composites is enhanced with the increase of paraffin content. In addition, the thermal insulation effect of pores also contributes to the increase of the maximum temperature difference between the outer and inner wall of phase change cementitious composites plate and the decrease of the maximum temperature of the cavity in the measurement system.
2018, 35(4): 989-998.
doi: 10.13801/j.cnki.fhclxb.20170706.003
Abstract:
To predict their lifespan of reconstituted bamboo products in practical use, X-ray computed tomography technology (X-CT) was employed and the standard of BS EN 1087-1:1995 was used as the hydrothermal aging condition of recombinant bamboo. The loss of structural strength was evaluated by the mathematical model of the CT value and the aging analysis indicators after hydrothermal aging of reconstituted bamboo. The results show that:the density, the internal bond strength and the CT value of recombinant bamboo are decreased after aging than before aging, and the differences are significant before and after aging. With the increasing of the aging time, the losses of the density, the internal bond strength and the CT value are increased and their changing trends are basically the same, which rapidly change in 1-2 h and gently change in 2.5-4.5 h and reach the peak at 4.5 h; the CT value difference and the density difference are fitted into linear model whose model correlation coefficient R2 and validation model R2 are 0.9270 and 0.9438, respectively, and the CT value difference and the internal bond strength difference are fitted into Allometric model whose model correlation coefficient R2 and validation model R2 are 0.9488 and 0.9439, respectively; the botanical characteristics of bamboo and the press technology of reconstituted bamboo cause the discretizing of the experimental data and the change of the discretizing before and after aging. The internal uniformity of reconstituted bamboo can be improved and the change of the discretizing before and after aging can be reduced by improving the press technology to enhance the prediction accuracy of the models.
To predict their lifespan of reconstituted bamboo products in practical use, X-ray computed tomography technology (X-CT) was employed and the standard of BS EN 1087-1:1995 was used as the hydrothermal aging condition of recombinant bamboo. The loss of structural strength was evaluated by the mathematical model of the CT value and the aging analysis indicators after hydrothermal aging of reconstituted bamboo. The results show that:the density, the internal bond strength and the CT value of recombinant bamboo are decreased after aging than before aging, and the differences are significant before and after aging. With the increasing of the aging time, the losses of the density, the internal bond strength and the CT value are increased and their changing trends are basically the same, which rapidly change in 1-2 h and gently change in 2.5-4.5 h and reach the peak at 4.5 h; the CT value difference and the density difference are fitted into linear model whose model correlation coefficient R2 and validation model R2 are 0.9270 and 0.9438, respectively, and the CT value difference and the internal bond strength difference are fitted into Allometric model whose model correlation coefficient R2 and validation model R2 are 0.9488 and 0.9439, respectively; the botanical characteristics of bamboo and the press technology of reconstituted bamboo cause the discretizing of the experimental data and the change of the discretizing before and after aging. The internal uniformity of reconstituted bamboo can be improved and the change of the discretizing before and after aging can be reduced by improving the press technology to enhance the prediction accuracy of the models.
2018, 35(4): 999-1013.
doi: 10.13801/j.cnki.fhclxb.20170712.001
Abstract:
The rubber asphalt was processed by the eight different matrix asphalts.The rubber asphalt zero shear viscosity(ZSV) was fitted by Cross flow, Carreau model and Matlab, Origin software.The correlation was analysised by the matrix four components and the rubber asphalt ZSV according to the grey correlation method theory.The rubber asphalt ZSV variability was discussed under different loading modes and the sensitive factors influencing the rubber asphalt ZSV were studied.The results show that the Cross model fitting degree to the rubber asphalt sample data is more than the Carreau model; The rubber asphalt ZSV is different fitted under the static load and dynamic load model; The repeated creep stage creep test fitting results and recovery phase fitting results are in the same magnitude order; The rubber asphalt ZSV measured by Brookfield viscosity decreases the increse of the test temperature; The correlation results of frequency scanning test, repeated creep test, different temperature and rubber asphalt rotary shear viscosity are consistent, namely that the aromatics are the strongest sensitivity according to ZSV of rubber asphalt.
The rubber asphalt was processed by the eight different matrix asphalts.The rubber asphalt zero shear viscosity(ZSV) was fitted by Cross flow, Carreau model and Matlab, Origin software.The correlation was analysised by the matrix four components and the rubber asphalt ZSV according to the grey correlation method theory.The rubber asphalt ZSV variability was discussed under different loading modes and the sensitive factors influencing the rubber asphalt ZSV were studied.The results show that the Cross model fitting degree to the rubber asphalt sample data is more than the Carreau model; The rubber asphalt ZSV is different fitted under the static load and dynamic load model; The repeated creep stage creep test fitting results and recovery phase fitting results are in the same magnitude order; The rubber asphalt ZSV measured by Brookfield viscosity decreases the increse of the test temperature; The correlation results of frequency scanning test, repeated creep test, different temperature and rubber asphalt rotary shear viscosity are consistent, namely that the aromatics are the strongest sensitivity according to ZSV of rubber asphalt.
2018, 35(4): 1014-1023.
doi: 10.13801/j.cnki.fhclxb.20170619.002
Abstract:
Based on the topology optimization method, the functional element topology optimization method was proposed to design a metamaterial and a functional element's structure with arbitrary negative Poisson's ratio. For different initial topological substrate structures of the functional element, including the rectangular and triangular initial topological substrate structure, with the specified negative Poisson's ratio as the constraint condition, the compliance of functional element was maximized as the objective function, and the topology optimization model with arbitrary negative Poisson's ratio was established and solved. The functional element was extracted by the topology optimal results, and the functional elements were periodically distributed to form a negative Poisson's structure. Then, the finite element model of the optimized metamaterial structure was established, and the Poisson's ratio of the functional element was calculated by the formula. Finally, the static and dynamic characteristics of the metamaterials were calculated and analyzed. The results demonstrate that this negative Poisson's ratio effect metamaterial specimen has good bearing capacity and has better vibration reduction performance in the middle and low frequency range.
Based on the topology optimization method, the functional element topology optimization method was proposed to design a metamaterial and a functional element's structure with arbitrary negative Poisson's ratio. For different initial topological substrate structures of the functional element, including the rectangular and triangular initial topological substrate structure, with the specified negative Poisson's ratio as the constraint condition, the compliance of functional element was maximized as the objective function, and the topology optimization model with arbitrary negative Poisson's ratio was established and solved. The functional element was extracted by the topology optimal results, and the functional elements were periodically distributed to form a negative Poisson's structure. Then, the finite element model of the optimized metamaterial structure was established, and the Poisson's ratio of the functional element was calculated by the formula. Finally, the static and dynamic characteristics of the metamaterials were calculated and analyzed. The results demonstrate that this negative Poisson's ratio effect metamaterial specimen has good bearing capacity and has better vibration reduction performance in the middle and low frequency range.
2018, 35(4): 1024-1031.
doi: 10.13801/j.cnki.fhclxb.20170628.003
Abstract:
First, on account of the shortcoming of relative low ability of resistance to the impact load for scarf repaired CFRP, surface based cohesive model(SCZM) and element based cohesive zone model (ECZM) were used to simulate laminates delamination and bondline damage, respectively. The impact response of CFRP and the evolution of two failures were investigated. Then, the influences of the impact energy, scarf angle and pre-tension were studied. Results indicate that the laminates delamination initiates prior to the bondline damage, which is independent of the applied impact energy. The bondline damage area increases much obviously than the laminates delamination with the increasing of impact energy. The scarf angle will significantly influence the bondline damage, while has almost no effect on the laminates delamination area. The pre-tension has negative effect on these two failures. At last, the effect of laminates delamination on bondline damage was further discussed by comparing with the situation that only considered bondline damage. The laminates delamination will reduce the damage area of bondline and delay the catastrophic failure of bondline.
First, on account of the shortcoming of relative low ability of resistance to the impact load for scarf repaired CFRP, surface based cohesive model(SCZM) and element based cohesive zone model (ECZM) were used to simulate laminates delamination and bondline damage, respectively. The impact response of CFRP and the evolution of two failures were investigated. Then, the influences of the impact energy, scarf angle and pre-tension were studied. Results indicate that the laminates delamination initiates prior to the bondline damage, which is independent of the applied impact energy. The bondline damage area increases much obviously than the laminates delamination with the increasing of impact energy. The scarf angle will significantly influence the bondline damage, while has almost no effect on the laminates delamination area. The pre-tension has negative effect on these two failures. At last, the effect of laminates delamination on bondline damage was further discussed by comparing with the situation that only considered bondline damage. The laminates delamination will reduce the damage area of bondline and delay the catastrophic failure of bondline.
