2016 Vol. 33, No. 6
2016, 33(6): 1147-1152.
doi: 10.13801/j.cnki.fhclxb.20160108.001
Abstract:
In order to study the hydro-thermal aging mechanism of glass fiber (GF)/epoxy composites, the effects of hydro-thermal aging on the properties of GF/epoxy 608 (EP608) composites were investigated by gravimetric method, dynamic mechanical analyzer (DMA), SEM and vector network dielectric analyzer firstly. Then, the relationships between moisture absorption ratio, mechanical properties, dielectric properties and aging time of the composites were analyzed, and the aging mechanism was discussed. The results show that with aging time increasing, both of the mechanical properties and dielectric properties for GF/EP608 composites reduce in different degrees. The effect of hydro-thermal aging on the moisture absorption ratio of GF/EP608 composites accords with Fickian diffusion law. The plasticization, hydrolyzation of resin matrix and the failure of fiber-matrix interface are the main reasons for the decrease of the mechanical properties and dielectric properties for GF/EP608 composites. The conclusions obtained can provide scientific references for the application of GF reinforced epoxy matrix composites.
In order to study the hydro-thermal aging mechanism of glass fiber (GF)/epoxy composites, the effects of hydro-thermal aging on the properties of GF/epoxy 608 (EP608) composites were investigated by gravimetric method, dynamic mechanical analyzer (DMA), SEM and vector network dielectric analyzer firstly. Then, the relationships between moisture absorption ratio, mechanical properties, dielectric properties and aging time of the composites were analyzed, and the aging mechanism was discussed. The results show that with aging time increasing, both of the mechanical properties and dielectric properties for GF/EP608 composites reduce in different degrees. The effect of hydro-thermal aging on the moisture absorption ratio of GF/EP608 composites accords with Fickian diffusion law. The plasticization, hydrolyzation of resin matrix and the failure of fiber-matrix interface are the main reasons for the decrease of the mechanical properties and dielectric properties for GF/EP608 composites. The conclusions obtained can provide scientific references for the application of GF reinforced epoxy matrix composites.
2016, 33(6): 1153-1160.
doi: 10.13801/j.cnki.fhclxb.20160317.004
Abstract:
We deal with analysis and prediction of the failure mechanism and the damage procedure of the multi-directional carbon fiber reinforced plastics (CFRP) laminates under the condition of low velocity impact with small energy based on the micro-mechanics of failure (MMF) theory. The impact damage behavior analysis method for the laminated structure was established based on MMF theory. During the process of impact loading, the constituent failure categories can be identified first by the MMF theory, then the comesponding material properties degradation scheme was applied to analyze the progressive failure of composites based on the constituent failure categories. Developed the user-defined material subroutine based on explicit analysis (VUMAT ) on the ABAQUS, it is a impact damage analysis program of laminate based on MMF theory. Finally, under the condition of low velocity impact with small energy, the failure mechanism and damage appearance of the multi-directional CFRP laminates was predicted based on impact damage behavior analysis method of MMF theory. The failure mechanisms and damage appearance obtained from both predicted results and test were compared, then the accuracy of the impact damage prediction method based on MMF theory were analyzed. The results show that the error between predicted pit diameter and test pit diameter is 4.8%,the predicted failure mechanism and damage appearance are consistent with the actual analysis.
We deal with analysis and prediction of the failure mechanism and the damage procedure of the multi-directional carbon fiber reinforced plastics (CFRP) laminates under the condition of low velocity impact with small energy based on the micro-mechanics of failure (MMF) theory. The impact damage behavior analysis method for the laminated structure was established based on MMF theory. During the process of impact loading, the constituent failure categories can be identified first by the MMF theory, then the comesponding material properties degradation scheme was applied to analyze the progressive failure of composites based on the constituent failure categories. Developed the user-defined material subroutine based on explicit analysis (VUMAT ) on the ABAQUS, it is a impact damage analysis program of laminate based on MMF theory. Finally, under the condition of low velocity impact with small energy, the failure mechanism and damage appearance of the multi-directional CFRP laminates was predicted based on impact damage behavior analysis method of MMF theory. The failure mechanisms and damage appearance obtained from both predicted results and test were compared, then the accuracy of the impact damage prediction method based on MMF theory were analyzed. The results show that the error between predicted pit diameter and test pit diameter is 4.8%,the predicted failure mechanism and damage appearance are consistent with the actual analysis.
2016, 33(6): 1161-1167.
doi: 10.13801/j.cnki.fhclxb.20160324.001
Abstract:
According to the structure characteristics and fiber layout characteristics of the satin woven composite T-joint manufacturing by resin transfer moulding (RTM), and based on the ANSYS finite element numerical analysis platform, geometric model and finite element model which conforms to the actual structure was set up. Based on the basic idea of progressive failure strength prediction method, the numerical analysis of a modified form of Hashin failure criteria was implemented using parametric design language (APDL) of the finite element analysis software ANSYS to develop the corresponding program. A progressive failure analysis model of 2D woven composites T-joints under bending load has been developed, which using an appropriate to evaluate ultimate failure. The method can efficiently simulate mechanical response and the initiation and propagation of damage of woven composite T-joints in the process from initial loading to ultimate failure, and predict the structural static strength.
According to the structure characteristics and fiber layout characteristics of the satin woven composite T-joint manufacturing by resin transfer moulding (RTM), and based on the ANSYS finite element numerical analysis platform, geometric model and finite element model which conforms to the actual structure was set up. Based on the basic idea of progressive failure strength prediction method, the numerical analysis of a modified form of Hashin failure criteria was implemented using parametric design language (APDL) of the finite element analysis software ANSYS to develop the corresponding program. A progressive failure analysis model of 2D woven composites T-joints under bending load has been developed, which using an appropriate to evaluate ultimate failure. The method can efficiently simulate mechanical response and the initiation and propagation of damage of woven composite T-joints in the process from initial loading to ultimate failure, and predict the structural static strength.
2016, 33(6): 1168-1173.
doi: 10.13801/j.cnki.fhclxb.20160107.003
Abstract:
Four kinds of poplar wood fibers (PWF, 125-180 μm, 180-425 μm, 425-850 μm and 850-2 000 μm)/high-density polyethylene (HDPE) composites were prepared by means of hot-compression molding. The flexural property test, impact property test, dynamic thermo-mechanical analysis(DMA), 24 h creep-24 h recovery test and 1 000 h long-term creep tests were performed for PWF/HDPE composites. The results show that the excessively large or small PWF size is not positively for improving the flexural property of PWF/HDPE composites. PWF/HDPE composites with fibers of 425-850 μm present the best enhancement effect. The flexural strength and the elastic modulus of 425-850 μm PWF/HDPE composites are 26.71 MPa and 2.73 GPa, respectively. Impact resistance property of PWF/HDPE composites keeps constant, while the PWF size increases from 180 μm to 2 000 μm. Whereas, 125-180 μm PWF/HDPE composites have the lowest impact resistance property. The PWF/HDPE composites with small fibers have the worst anti-creep performance, indicating that it is not suitable for long-term loading. 850-2 000 μm PWF/HDPE composites with long fibers have outstanding long-term anti-creep performance and recovery (78.46%), and its 1 000 h deformation is just 0.809 mm, which compares with the average values of 1 000 h deformation for other PWF/HDPE composites and decreases by 48.00%.
Four kinds of poplar wood fibers (PWF, 125-180 μm, 180-425 μm, 425-850 μm and 850-2 000 μm)/high-density polyethylene (HDPE) composites were prepared by means of hot-compression molding. The flexural property test, impact property test, dynamic thermo-mechanical analysis(DMA), 24 h creep-24 h recovery test and 1 000 h long-term creep tests were performed for PWF/HDPE composites. The results show that the excessively large or small PWF size is not positively for improving the flexural property of PWF/HDPE composites. PWF/HDPE composites with fibers of 425-850 μm present the best enhancement effect. The flexural strength and the elastic modulus of 425-850 μm PWF/HDPE composites are 26.71 MPa and 2.73 GPa, respectively. Impact resistance property of PWF/HDPE composites keeps constant, while the PWF size increases from 180 μm to 2 000 μm. Whereas, 125-180 μm PWF/HDPE composites have the lowest impact resistance property. The PWF/HDPE composites with small fibers have the worst anti-creep performance, indicating that it is not suitable for long-term loading. 850-2 000 μm PWF/HDPE composites with long fibers have outstanding long-term anti-creep performance and recovery (78.46%), and its 1 000 h deformation is just 0.809 mm, which compares with the average values of 1 000 h deformation for other PWF/HDPE composites and decreases by 48.00%.
2016, 33(6): 1174-1178.
doi: 10.13801/j.cnki.fhclxb.20160107.004
Abstract:
Poplar wood fibers (PWF) of 850-2 000 μm reinforced high-density polyethylene (HDPE) composites were prepared by compression molding process. The flexural mechanical property test, un-notched beam impact strength test, 24 h flexural creep-24 h recovery property test, 1 000 h creep property test and residual flexural mechanical performance test after creep of PWF/HDPE composites were studied. And two-parameter exponential model, Findley's exponential model and four-element Burgers model were used to fit creep curve. The results show that the flexural strength, elastic modulus and un-notched impact strength of PWF/HDPE composites are 21.14 MPa, 2.31 GPa and 6.77 kJ/m2, respectively. The 24 h deformation is 0.803 mm, and 24 h recovery rate is 78.46%. After creep, flexural strength decreases by 6.45%, but the elastic modulus increases by 8.95%. The 1 000 h deformation is 0.809 mm, and the flexural strength of the creep is 72.35% of the original value, and the elastic modulus increases by 10.67%. Among the three models, four-element Burgers model successfully simulates with the creep properties of PWF/HDPE composites.
Poplar wood fibers (PWF) of 850-2 000 μm reinforced high-density polyethylene (HDPE) composites were prepared by compression molding process. The flexural mechanical property test, un-notched beam impact strength test, 24 h flexural creep-24 h recovery property test, 1 000 h creep property test and residual flexural mechanical performance test after creep of PWF/HDPE composites were studied. And two-parameter exponential model, Findley's exponential model and four-element Burgers model were used to fit creep curve. The results show that the flexural strength, elastic modulus and un-notched impact strength of PWF/HDPE composites are 21.14 MPa, 2.31 GPa and 6.77 kJ/m2, respectively. The 24 h deformation is 0.803 mm, and 24 h recovery rate is 78.46%. After creep, flexural strength decreases by 6.45%, but the elastic modulus increases by 8.95%. The 1 000 h deformation is 0.809 mm, and the flexural strength of the creep is 72.35% of the original value, and the elastic modulus increases by 10.67%. Among the three models, four-element Burgers model successfully simulates with the creep properties of PWF/HDPE composites.
2016, 33(6): 1179-1185.
doi: 10.13801/j.cnki.fhclxb.20151201.004
Abstract:
Nano MgO particles without hydroxyl group (—OH) on surface were prepared through hydrothermal method, and 10wt% MgO/low density polyethylene (LDPE) composites were prepared by master batch method. The space charge characteristics of nano MgO/LDPE composites under 70 kV/mm direct current fields were studied. The dispersion effect of nanoparticles and the application promotional value in industry of this method were also evaluated. The results show that the effects of surface hydroxy on variable temperature volume resistivity and dielectric properties of nano MgO/LDPE composites were not remarkable, while space charge accumulates increase. When the concentration of nano MgO is 1wt%, composite presentes the excellent electrical properties.
Nano MgO particles without hydroxyl group (—OH) on surface were prepared through hydrothermal method, and 10wt% MgO/low density polyethylene (LDPE) composites were prepared by master batch method. The space charge characteristics of nano MgO/LDPE composites under 70 kV/mm direct current fields were studied. The dispersion effect of nanoparticles and the application promotional value in industry of this method were also evaluated. The results show that the effects of surface hydroxy on variable temperature volume resistivity and dielectric properties of nano MgO/LDPE composites were not remarkable, while space charge accumulates increase. When the concentration of nano MgO is 1wt%, composite presentes the excellent electrical properties.
2016, 33(6): 1192-1197.
doi: 10.13801/j.cnki.fhclxb.20160107.006
Abstract:
Cationic polyelectrolyte poly(diallyldimethylammonium chloride)(PDDA) was used to modify SiO2, and SiO2-PDDA-graphite oxide (GO) core-shell hybrid particles were prepared by electrostatic self-assembly. By introducing SiO2-PDDA-GO into high-temperature vulcanization silicone rubber (SR)with solution blending method, SiO2-PDDA-GO/SR dielectric elastomer composites were prepared. Results show that this method can realize GO large surface coating on surface of SiO2 to prevent GO from self-agglomerating. GO core-shell hybrid particles/SR composites were obtained without in-situ thermal reduction because PDDA can reduce GO, made experimental scheme simple and environmental protection. The dielectric constant of SiO2-PDDA-GO/SR dielectric composite at 100 Hz increases to 21.53 with 60wt% SiO2-PDDA-GO which is 11.6 times than SR, and dielectric loss remains at low level. Meanwhile, modulus of composites remains low level. The lateral actuation strain of SiO2-PDDA-GO/SR dielectric elastomer composites with 60wt% SiO2-PDDA-GO at 2.48 kV/mm compared with pure SR increases 15 fold under same electric field intensity.
Cationic polyelectrolyte poly(diallyldimethylammonium chloride)(PDDA) was used to modify SiO2, and SiO2-PDDA-graphite oxide (GO) core-shell hybrid particles were prepared by electrostatic self-assembly. By introducing SiO2-PDDA-GO into high-temperature vulcanization silicone rubber (SR)with solution blending method, SiO2-PDDA-GO/SR dielectric elastomer composites were prepared. Results show that this method can realize GO large surface coating on surface of SiO2 to prevent GO from self-agglomerating. GO core-shell hybrid particles/SR composites were obtained without in-situ thermal reduction because PDDA can reduce GO, made experimental scheme simple and environmental protection. The dielectric constant of SiO2-PDDA-GO/SR dielectric composite at 100 Hz increases to 21.53 with 60wt% SiO2-PDDA-GO which is 11.6 times than SR, and dielectric loss remains at low level. Meanwhile, modulus of composites remains low level. The lateral actuation strain of SiO2-PDDA-GO/SR dielectric elastomer composites with 60wt% SiO2-PDDA-GO at 2.48 kV/mm compared with pure SR increases 15 fold under same electric field intensity.
2016, 33(6): 1198-1205.
doi: 10.13801/j.cnki.fhclxb.20151228.001
Abstract:
As one of dielectric materials for embedded capacitors, Al powder/polymer composites have good application potentials due to low cost, easy processability and high dielectric constant. To lower the dielectric loss of these materials, the secondary passivation processes of Al flakes using air and tiny water respectively as the oxidants were studied. The structure and chemical composition of passivation films were characterized, and dielectric properties were evaluated for the passivated Al flakes and their polytetrafluoroethylene (PTFE) composites. The results show that several-nanometer thick secondary passivated film forms outside the self-passivated film of Al flakes, mainly consisting of Al2O3 and Al(OH)3. The former contains main Al2O3, and the latter contains main Al(OH)3. Air passivation occurs very slowly, the resulting secondary passivated films are thin but smooth, in contrast, tiny-water passivation proceeds quickly; the resulting ones are thick but loose. Tiny-water passivation exhibits better applicability in tailoring the thickness of passivated films than air passivation, so as to adjust the dielectric properties of Al flakes/PTFE composites.
As one of dielectric materials for embedded capacitors, Al powder/polymer composites have good application potentials due to low cost, easy processability and high dielectric constant. To lower the dielectric loss of these materials, the secondary passivation processes of Al flakes using air and tiny water respectively as the oxidants were studied. The structure and chemical composition of passivation films were characterized, and dielectric properties were evaluated for the passivated Al flakes and their polytetrafluoroethylene (PTFE) composites. The results show that several-nanometer thick secondary passivated film forms outside the self-passivated film of Al flakes, mainly consisting of Al2O3 and Al(OH)3. The former contains main Al2O3, and the latter contains main Al(OH)3. Air passivation occurs very slowly, the resulting secondary passivated films are thin but smooth, in contrast, tiny-water passivation proceeds quickly; the resulting ones are thick but loose. Tiny-water passivation exhibits better applicability in tailoring the thickness of passivated films than air passivation, so as to adjust the dielectric properties of Al flakes/PTFE composites.
2016, 33(6): 1206-1213.
doi: 10.13801/j.cnki.fhclxb.20160122.001
Abstract:
The high-temperature mechanical properties of carbon fiber reinforced polyimide resin matrix composites MT300/KH420 were studied, during which the tensile and interlaminar shear performance variation rule of MT300/KH420 laminates with[0°]7, [0°]14 and [±45°/0°/90°/+45°/0°2]s fiber orientations were especially analyzed at temperature ranging from ambient temperature to 500 ℃. Results show that tensile strength of [0°]7 laminate shows an increase while tensile modulus changes little with the increase of temperature until 350 ℃. At 420 ℃ tensile strength and modulus reduce significantly, and at 500 ℃, 65% and 83% of their pristine values remain, exhibiting an excellent high-temperature tensile property. As temperature rises, interlaminar shear strength of MT300/KH420 laminates with[0°]14 degrades continuously from ambient temperature to 420 ℃ where a retention rate of 52.8% is observed. A viscoelastic effect occurs at high temperature, especially at 420 ℃ it turns to be the most severest. Compared with unidirectional laminates, [±45°/0°/90°/+45°/0°2]s multidirectional laminates show more stable high-temperature mechanical properties. Mechanical properties of fiber-dominated longitudinal specimen are less dependent on temperature.
The high-temperature mechanical properties of carbon fiber reinforced polyimide resin matrix composites MT300/KH420 were studied, during which the tensile and interlaminar shear performance variation rule of MT300/KH420 laminates with[0°]7, [0°]14 and [±45°/0°/90°/+45°/0°2]s fiber orientations were especially analyzed at temperature ranging from ambient temperature to 500 ℃. Results show that tensile strength of [0°]7 laminate shows an increase while tensile modulus changes little with the increase of temperature until 350 ℃. At 420 ℃ tensile strength and modulus reduce significantly, and at 500 ℃, 65% and 83% of their pristine values remain, exhibiting an excellent high-temperature tensile property. As temperature rises, interlaminar shear strength of MT300/KH420 laminates with[0°]14 degrades continuously from ambient temperature to 420 ℃ where a retention rate of 52.8% is observed. A viscoelastic effect occurs at high temperature, especially at 420 ℃ it turns to be the most severest. Compared with unidirectional laminates, [±45°/0°/90°/+45°/0°2]s multidirectional laminates show more stable high-temperature mechanical properties. Mechanical properties of fiber-dominated longitudinal specimen are less dependent on temperature.
2016, 33(6): 1214-1222.
doi: 10.13801/j.cnki.fhclxb.20160304.002
Abstract:
Based on the automated fiber placement(AFP)in-situ curing technology of thermoplastic composite (TPC), we researched AFP system technology of thermoplastic composites, analyzed the functional requirements of AFP platform, proposed the overall planning scheme of platform, designed and developed the automatic prototype head of thermoplastic composites, meanwhile, proposed the schemes of tension control for prepreg, precise sending prepreg and closed-loop control for temperature. On this basis, feasibility verification experiments for the AFP system have been carried out to testify feasibility of the planning scheme and practical value of the platform. The results show that the experimental platform optimizes the matching of tension and laying speed, realizes the dynamic constant tension laying of prepreg and ensures the quality of the molding component according to the laying characteristics of thermoplastic composites. The experimental platform regulates the coordination of laying speed and sending prepreg to achieve precise positioning and security molding component size. The relationship between laying speed, heat power and heat flux distribution was established to realize high precision temperature field distribution control. Although the mechanical properties for AFP molding component are lower than those of hot moulded component, the AFP platform will lay foundation for wide use of AFP system technology in thermoplastic composites.
Based on the automated fiber placement(AFP)in-situ curing technology of thermoplastic composite (TPC), we researched AFP system technology of thermoplastic composites, analyzed the functional requirements of AFP platform, proposed the overall planning scheme of platform, designed and developed the automatic prototype head of thermoplastic composites, meanwhile, proposed the schemes of tension control for prepreg, precise sending prepreg and closed-loop control for temperature. On this basis, feasibility verification experiments for the AFP system have been carried out to testify feasibility of the planning scheme and practical value of the platform. The results show that the experimental platform optimizes the matching of tension and laying speed, realizes the dynamic constant tension laying of prepreg and ensures the quality of the molding component according to the laying characteristics of thermoplastic composites. The experimental platform regulates the coordination of laying speed and sending prepreg to achieve precise positioning and security molding component size. The relationship between laying speed, heat power and heat flux distribution was established to realize high precision temperature field distribution control. Although the mechanical properties for AFP molding component are lower than those of hot moulded component, the AFP platform will lay foundation for wide use of AFP system technology in thermoplastic composites.
2016, 33(6): 1223-1233.
doi: 10.13801/j.cnki.fhclxb.20160107.002
Abstract:
The accelerated neutral salt spray aging test was used to simulate the marine atmospheric environment, and the flexural properties of glass fiber/unsaturated polyester composites in salt spray environment were investigated. Through changes in moisture absorption rate, glass transition temperature, Barcol hardness and bending properties of glass fiber/unsaturated polyester composites after salt spray acceleration aging, in addition with the corrosion depths obtained by metallographic microscope, the effects of corrosion depth on durability of glass fiber/unsaturated polyester composites were studied. The results indicate that the moisture absorption of glass fiber/unsaturated polyester composites increases quickly with time in the early aging stage, and tends to be stable at last. Glass transition temperature of glass fiber/unsaturated polyester composites firstly increases, then decreases. After 180 d of aging time, the glass transition temperature increases by 2.1%. After 180 d of aging time, the Barcol hardness decreases by 17.6% compared to the un-aged one and flexural strengths loss rate is 10%. Based on the corrosion depths obtained by metallographic microscope analysis, the relationship between the corrosion depths and flexural strength was established for glass fiber/unsaturated polyester composites.
The accelerated neutral salt spray aging test was used to simulate the marine atmospheric environment, and the flexural properties of glass fiber/unsaturated polyester composites in salt spray environment were investigated. Through changes in moisture absorption rate, glass transition temperature, Barcol hardness and bending properties of glass fiber/unsaturated polyester composites after salt spray acceleration aging, in addition with the corrosion depths obtained by metallographic microscope, the effects of corrosion depth on durability of glass fiber/unsaturated polyester composites were studied. The results indicate that the moisture absorption of glass fiber/unsaturated polyester composites increases quickly with time in the early aging stage, and tends to be stable at last. Glass transition temperature of glass fiber/unsaturated polyester composites firstly increases, then decreases. After 180 d of aging time, the glass transition temperature increases by 2.1%. After 180 d of aging time, the Barcol hardness decreases by 17.6% compared to the un-aged one and flexural strengths loss rate is 10%. Based on the corrosion depths obtained by metallographic microscope analysis, the relationship between the corrosion depths and flexural strength was established for glass fiber/unsaturated polyester composites.
2016, 33(6): 1234-1241.
doi: 10.13801/j.cnki.fhclxb.20160413.005
Abstract:
New type of integrated stitch sandwich structure was designed. The integrated stitched sandwich structure composites were prepared by vacuum infusion molding process (VIMP) to investigate the mechanical performance and failure mode under the flatwise compression load. Finite element model was established to study the effects of the stitching yarn consumption on flatwise compression mechanical properties of integrated stitched sandwich structure composites. The results indicate that the new type of integrated stitch sandwich structure composites can improve the number of yarns and avoid the disadvantages of fiber cross damage caused by the traditional angled stitched. The compression strength and compression modulus of integrated stitched sandwich structure composites increase with the increase of the number of stitching yarn. However the specific compression strength will decrease when the number of stitching yarn is high. The rationality of the established finite element model is validated by comparing with numerical calculation results and test results. It indicates that the model could be used to predict the compression modulus.
New type of integrated stitch sandwich structure was designed. The integrated stitched sandwich structure composites were prepared by vacuum infusion molding process (VIMP) to investigate the mechanical performance and failure mode under the flatwise compression load. Finite element model was established to study the effects of the stitching yarn consumption on flatwise compression mechanical properties of integrated stitched sandwich structure composites. The results indicate that the new type of integrated stitch sandwich structure composites can improve the number of yarns and avoid the disadvantages of fiber cross damage caused by the traditional angled stitched. The compression strength and compression modulus of integrated stitched sandwich structure composites increase with the increase of the number of stitching yarn. However the specific compression strength will decrease when the number of stitching yarn is high. The rationality of the established finite element model is validated by comparing with numerical calculation results and test results. It indicates that the model could be used to predict the compression modulus.
2016, 33(6): 1242-1250.
doi: 10.13801/j.cnki.fhclxb.20160315.009
Abstract:
A general and semi-empirical model was developed to predict the tensile strength of multidirectional composite laminates with open-holes using the finite fracture mechanics method. Both stress-based and energy-based failure criteria were used to predict failure in this model. The ply elastic constants, the laminate unnotched strength and the fracture toughness of 0° plies were the only material properties required by the model. The relation between fracture toughness of multidirectional composite laminate and that of 0° plies was established based on linear fracture mechanics. The strength of an open-hole composite laminate with any fiber dominated lay-ups was predicted. The model was validated by comparing its prediction results with test data of open-hole composite laminates. The maximum predicting error is 9.7%. The model was also compared with point stress method and average stress method and results show that the present model provides more accurate predictions than the traditronal length method.
A general and semi-empirical model was developed to predict the tensile strength of multidirectional composite laminates with open-holes using the finite fracture mechanics method. Both stress-based and energy-based failure criteria were used to predict failure in this model. The ply elastic constants, the laminate unnotched strength and the fracture toughness of 0° plies were the only material properties required by the model. The relation between fracture toughness of multidirectional composite laminate and that of 0° plies was established based on linear fracture mechanics. The strength of an open-hole composite laminate with any fiber dominated lay-ups was predicted. The model was validated by comparing its prediction results with test data of open-hole composite laminates. The maximum predicting error is 9.7%. The model was also compared with point stress method and average stress method and results show that the present model provides more accurate predictions than the traditronal length method.
2016, 33(6): 1251-1258.
doi: 10.13801/j.cnki.fhclxb.20151209.005
Abstract:
Carbon fiber reinforced carbon aerogel composites were prepared by impregnating the fiber preform, gel aging, supercritical drying and carbonization. Resorcinol (R)-furfural (F) alcohol sol was synthesized by isopropanol (I) as solvent, hexamethylenetetramine (H) as catalyst. The effects of sol proportion on densities, microstructures and mechanical properties of carbon fiber reinforced carbon aerogel insulation composites were investigated. The results show that the densities of carbon fiber reinforced carbon aerogel insulation composites decrease gradually, the pores diameter and the amount of large pores in matrix carbon aerogels and the interface formed with carbon fiber increase, the strength of carbon fiber reinforced carbon aerogel insulation composites decreases with the increases of amount of substance ratio for isopropanol and resorcinol. When isopropanol and resorcinol amount of substance ratio increases from 18 to 28, the compressive strength decreases from 2.498 MPa (strain 10%)to 0.716 MPa (strain 10%), tensile strenghth decreases from 2.019 MPa to 1.001 MPa, bending strength decreases from 3.984 MPa to 1.818 MPa. The densities of carbon fiber reinforced carbon aerogel insulation composites increases firstly and then decreases, the pores diameter and the the amount of large pores in matrix carbon aerogels and interface formed with carbon fiber decreases firstly and then increases, the strength of carbon fiber reinforced carbon aerogel insulation composites increases fistly and then decreases with the increase of amount of substance ratio for hexamethylenetetramine and resorcinol. The densities and the strength of carbon fiber reinforced carbon aerogel insulation composites are biggest when amount of substance ratio for hexamethylenetetramine and resorcinol is 0.008 5, the compressive strength is 1.066 MPa (strain 10%), the tensile strenghth is 1.256 MPa, bending strength is 3.556 MPa.
Carbon fiber reinforced carbon aerogel composites were prepared by impregnating the fiber preform, gel aging, supercritical drying and carbonization. Resorcinol (R)-furfural (F) alcohol sol was synthesized by isopropanol (I) as solvent, hexamethylenetetramine (H) as catalyst. The effects of sol proportion on densities, microstructures and mechanical properties of carbon fiber reinforced carbon aerogel insulation composites were investigated. The results show that the densities of carbon fiber reinforced carbon aerogel insulation composites decrease gradually, the pores diameter and the amount of large pores in matrix carbon aerogels and the interface formed with carbon fiber increase, the strength of carbon fiber reinforced carbon aerogel insulation composites decreases with the increases of amount of substance ratio for isopropanol and resorcinol. When isopropanol and resorcinol amount of substance ratio increases from 18 to 28, the compressive strength decreases from 2.498 MPa (strain 10%)to 0.716 MPa (strain 10%), tensile strenghth decreases from 2.019 MPa to 1.001 MPa, bending strength decreases from 3.984 MPa to 1.818 MPa. The densities of carbon fiber reinforced carbon aerogel insulation composites increases firstly and then decreases, the pores diameter and the the amount of large pores in matrix carbon aerogels and interface formed with carbon fiber decreases firstly and then increases, the strength of carbon fiber reinforced carbon aerogel insulation composites increases fistly and then decreases with the increase of amount of substance ratio for hexamethylenetetramine and resorcinol. The densities and the strength of carbon fiber reinforced carbon aerogel insulation composites are biggest when amount of substance ratio for hexamethylenetetramine and resorcinol is 0.008 5, the compressive strength is 1.066 MPa (strain 10%), the tensile strenghth is 1.256 MPa, bending strength is 3.556 MPa.
2016, 33(6): 1259-1265.
doi: 10.13801/j.cnki.fhclxb.20151127.003
Abstract:
The Cf/HfC composite was prepared by liquid impregnation combined reactive melt infiltration technique. The impregnation efficiency, anti-oxidant and anti-ablation particles distribution morphology, infiltration efficiency and infiltration organization were studied, the antioxidant ablation property and mechanical properties of Cf/HfC composites were also assessed. Results show that the modified C/C preform which contains 13wt% ZrB2+HfO2+TaSi2 particles was obtained after five cycles of impregnation-carbonization and one high-temperature treatment process, the density and open porosity of which are 1.41 g/cm3 and 24.84%, respectively. Particles are mainly distributed in matrix carbon between fiber bundles, and the distribution is uniform. The Cf/HfC composites whose density and open porosity are 2.98 g/cm3 and 12.95%, was prepared after Hf35Zr10Si5Ta alloy reactively melt infiltrated modified C/C perform. The linear ablation rate is 0.017 1 mm/s, the flexural strength is 173.76 MPa, and the fracture mechanism is pseudo-ductile fracture.
The Cf/HfC composite was prepared by liquid impregnation combined reactive melt infiltration technique. The impregnation efficiency, anti-oxidant and anti-ablation particles distribution morphology, infiltration efficiency and infiltration organization were studied, the antioxidant ablation property and mechanical properties of Cf/HfC composites were also assessed. Results show that the modified C/C preform which contains 13wt% ZrB2+HfO2+TaSi2 particles was obtained after five cycles of impregnation-carbonization and one high-temperature treatment process, the density and open porosity of which are 1.41 g/cm3 and 24.84%, respectively. Particles are mainly distributed in matrix carbon between fiber bundles, and the distribution is uniform. The Cf/HfC composites whose density and open porosity are 2.98 g/cm3 and 12.95%, was prepared after Hf35Zr10Si5Ta alloy reactively melt infiltrated modified C/C perform. The linear ablation rate is 0.017 1 mm/s, the flexural strength is 173.76 MPa, and the fracture mechanism is pseudo-ductile fracture.
2016, 33(6): 1266-1273.
doi: 10.13801/j.cnki.fhclxb.20151228.002
Abstract:
The interphase modified coating plays a vital role in adjusting the mechanical properties of composites, in particular for those Cf/SiC composites prepared from the gaseous silicon infiltration (GSI) process. The ideal interphase modified coating should not only prevent the etching of C fiber by Si vapor, but also render a good interface bonding between C fiber and SiC matrix. With SiC coatings from the precursor infiltration-pyrolysis (PIP) route as the interphase modified coating in 3D-C fiber preform, we discuss the effects of PIP-SiC coating on mechanical properties of Cf/SiC composites made from GSI. The results show that, without coating modification, the GSI Cf/SiC composites have poor mechanical properties and show brittle fracture characteristic, with the flexure strength, flexure modulus and fracture toughness 87.6 MPa, 56.9 GPa and 2.1 MPa·m1/2, respectively. Those composites with PIP-SiC interphase modified coating exhibit better mechanical properties, with PIP-SiC coating modification, with the increase of the PIP-SiC cycles, flexure strength, flexure modulus and fracture toughness of GSI Cf/SiC composites decrease, in particular those with the PIP-SiC coatings after one cycle, with the flexure strength, flexure modulus and fracture toughness 185.2 MPa, 91.1 GPa and 5.5 MPa·m1/2, respectively. The improvement effects from the PIP-SiC interphase modified coating are attributed to the transfer loading and prevention of etching by Si.
The interphase modified coating plays a vital role in adjusting the mechanical properties of composites, in particular for those Cf/SiC composites prepared from the gaseous silicon infiltration (GSI) process. The ideal interphase modified coating should not only prevent the etching of C fiber by Si vapor, but also render a good interface bonding between C fiber and SiC matrix. With SiC coatings from the precursor infiltration-pyrolysis (PIP) route as the interphase modified coating in 3D-C fiber preform, we discuss the effects of PIP-SiC coating on mechanical properties of Cf/SiC composites made from GSI. The results show that, without coating modification, the GSI Cf/SiC composites have poor mechanical properties and show brittle fracture characteristic, with the flexure strength, flexure modulus and fracture toughness 87.6 MPa, 56.9 GPa and 2.1 MPa·m1/2, respectively. Those composites with PIP-SiC interphase modified coating exhibit better mechanical properties, with PIP-SiC coating modification, with the increase of the PIP-SiC cycles, flexure strength, flexure modulus and fracture toughness of GSI Cf/SiC composites decrease, in particular those with the PIP-SiC coatings after one cycle, with the flexure strength, flexure modulus and fracture toughness 185.2 MPa, 91.1 GPa and 5.5 MPa·m1/2, respectively. The improvement effects from the PIP-SiC interphase modified coating are attributed to the transfer loading and prevention of etching by Si.
2016, 33(6): 1274-1280.
doi: 10.13801/j.cnki.fhclxb.20160129.002
Abstract:
In order to research the toughness characteristics of hybrid fiber on ultra-high performance concrete(UHPC), 161 specimens of three-point bending beam fracture testing of UHPC reinforced with four type fibers and various contents have been conducted. The load-crack mouth open displacement (CMOD) curves and load-deflection curves were measured. We took the peak-load CMOD of plain UHPC as the reference initial CMOD value of hybrid fibers reinforced UHPC. Based on the load-CMOD curves, a characterization method of equivalent fracture toughness was proposed. This new method has clear physical meaning, and unveils the influence rule of hybrid fibers type and contents to fracture toughness of UHPC. The research shows that the toughness of UHPC depends on the content of steel fiber in small deformation stage (less than the 50 times CMOD value of plain UHPC at peak load) and macro-synthetic fiber plays toughening effect in middle deformation and large deformation stage (larger than the 50 times CMOD value of plain UHPC at peak load).
In order to research the toughness characteristics of hybrid fiber on ultra-high performance concrete(UHPC), 161 specimens of three-point bending beam fracture testing of UHPC reinforced with four type fibers and various contents have been conducted. The load-crack mouth open displacement (CMOD) curves and load-deflection curves were measured. We took the peak-load CMOD of plain UHPC as the reference initial CMOD value of hybrid fibers reinforced UHPC. Based on the load-CMOD curves, a characterization method of equivalent fracture toughness was proposed. This new method has clear physical meaning, and unveils the influence rule of hybrid fibers type and contents to fracture toughness of UHPC. The research shows that the toughness of UHPC depends on the content of steel fiber in small deformation stage (less than the 50 times CMOD value of plain UHPC at peak load) and macro-synthetic fiber plays toughening effect in middle deformation and large deformation stage (larger than the 50 times CMOD value of plain UHPC at peak load).
2016, 33(6): 1281-1286.
doi: 10.13801/j.cnki.fhclxb.20160128.002
Abstract:
The effects of introduction methods of SiC on TEM structure and mechanical properties of 20wt% nano SiC/MoSi2 composites prepared by reactive melt infiltration were studied. The results show that, the nanometer scale of matrix phase and reinforced phase of SiC/MoSi2 composites can be obtained in the process of complete in-situ reactive infiltration silicon, but maybe due to the large number of fault defects inner crystals of the structure, the mechanical properties of the nano SiC/MoSi2 composites improve not too much; when preparing the composites in partial in-situ reactive melt infiltration method to relieve the severe phase reaction, the defects inner crystal in nano SiC/MoSi2 composites disappear, and there are a large number of tear ridges in the fracture, also, the mechanical properties of composites increase obviously due to the introduction of SiC initial powder.
The effects of introduction methods of SiC on TEM structure and mechanical properties of 20wt% nano SiC/MoSi2 composites prepared by reactive melt infiltration were studied. The results show that, the nanometer scale of matrix phase and reinforced phase of SiC/MoSi2 composites can be obtained in the process of complete in-situ reactive infiltration silicon, but maybe due to the large number of fault defects inner crystals of the structure, the mechanical properties of the nano SiC/MoSi2 composites improve not too much; when preparing the composites in partial in-situ reactive melt infiltration method to relieve the severe phase reaction, the defects inner crystal in nano SiC/MoSi2 composites disappear, and there are a large number of tear ridges in the fracture, also, the mechanical properties of composites increase obviously due to the introduction of SiC initial powder.
2016, 33(6): 1287-1296.
doi: 10.13801/j.cnki.fhclxb.20160328.009
Abstract:
Based on the CT scan results of 3D four-directional braided ceramic-matrix composites and theoretical analysis, referred to the existing interlaced model, an improved 3D cell element model was established. This model truly reflects the mesoscopic structure of the internal material. The yarns' cross-section along their axes model varied cyclically in shape and area, yarn's cross-sections alternate transformed form parallelograms to pentagons, each yarn's axis presented interlaced relationships, close to the extrusion deformation law of tight yarns in materials. By measuring the average yarn packing factor and using the finite element method, the elastic properties of yarns and materials were obtained. The predicted value agrees well with the test data. The finite element simulation reveals that the yarns undertake the main load in the materials' cell model. Some of the yarns and matrixes interfaces tend to appear stress concentration phenomenon. These areas could mostly produce crack propagations and local damages. The determination of the mesoscopic stress field also provides a foundation for the analysis of failure mechanism and the strength of the materials.
Based on the CT scan results of 3D four-directional braided ceramic-matrix composites and theoretical analysis, referred to the existing interlaced model, an improved 3D cell element model was established. This model truly reflects the mesoscopic structure of the internal material. The yarns' cross-section along their axes model varied cyclically in shape and area, yarn's cross-sections alternate transformed form parallelograms to pentagons, each yarn's axis presented interlaced relationships, close to the extrusion deformation law of tight yarns in materials. By measuring the average yarn packing factor and using the finite element method, the elastic properties of yarns and materials were obtained. The predicted value agrees well with the test data. The finite element simulation reveals that the yarns undertake the main load in the materials' cell model. Some of the yarns and matrixes interfaces tend to appear stress concentration phenomenon. These areas could mostly produce crack propagations and local damages. The determination of the mesoscopic stress field also provides a foundation for the analysis of failure mechanism and the strength of the materials.
2016, 33(6): 1297-1304.
doi: 10.13801/j.cnki.fhclxb.20160602.001
Abstract:
In order to investigate the tensile and interlaminar shear properties of mullite fiber reinforced SiO2 aerogel composites, related tests were conducted. The in-plane tension tests of the composites were carried out at room temperature firstly, and the in-plane tensile modulus of the composite at room temperature was obtained. Then, the extensometer method and digital image correlation method were adopted respectively to measure the tensile deformations, and the two methods were compared and analyzed. Finally, the interlaminar shear tests at different temperatures were conducted, the interlaminar shear properties of the composites at different temperatures were investigated, and the microstructures were analyzed. The results show that the tension modulus of the composites is about 285.17 MPa. The tensile modulus calculated by the tensile deformation obtained by the extensometer method is 2.4% higher than the tensile modulus obtained by the digital image correlation method. The specimens present obvious interlaminar shear damage at room temperature and high temperature. The microscopic analyses on composites find that SiO2 aerogel matrix mainly distributes in interlaminar areas and reinforced fibers mainly distributes in plies. The conclusions obtained show that the tensile and interlaminar properties of mullite fiber reinforced SiO2 aerogel composites are relatively poor, SiO2 aerogel matrix plays a main role under interlaminar shear load, and temperature has a great influence on the properties of the composites.
In order to investigate the tensile and interlaminar shear properties of mullite fiber reinforced SiO2 aerogel composites, related tests were conducted. The in-plane tension tests of the composites were carried out at room temperature firstly, and the in-plane tensile modulus of the composite at room temperature was obtained. Then, the extensometer method and digital image correlation method were adopted respectively to measure the tensile deformations, and the two methods were compared and analyzed. Finally, the interlaminar shear tests at different temperatures were conducted, the interlaminar shear properties of the composites at different temperatures were investigated, and the microstructures were analyzed. The results show that the tension modulus of the composites is about 285.17 MPa. The tensile modulus calculated by the tensile deformation obtained by the extensometer method is 2.4% higher than the tensile modulus obtained by the digital image correlation method. The specimens present obvious interlaminar shear damage at room temperature and high temperature. The microscopic analyses on composites find that SiO2 aerogel matrix mainly distributes in interlaminar areas and reinforced fibers mainly distributes in plies. The conclusions obtained show that the tensile and interlaminar properties of mullite fiber reinforced SiO2 aerogel composites are relatively poor, SiO2 aerogel matrix plays a main role under interlaminar shear load, and temperature has a great influence on the properties of the composites.
2016, 33(6): 1305-1310.
doi: 10.13801/j.cnki.fhclxb.20160315.014
Abstract:
By applying the impedance matching technique and using metallic wire grid electrical tunable unit, the optimization design of electrical tunable was performed for plate joints (or reinforcing rib) in large partitioning dielectric radome. On the premise of guaranteeing mechanical performance of joint structure, the transmission efficiency of optimized mixed dielectric structure containing metallic wire grids improves by about 20% compared with plate joints. In addition, by loading different metallic wire grids, the frequency range of best transmission for mixed structure can be adjusted, thus can be used to develop radomes of various frequency. This provides a novel technological pathway to design high-performance large dielectric radomes.
By applying the impedance matching technique and using metallic wire grid electrical tunable unit, the optimization design of electrical tunable was performed for plate joints (or reinforcing rib) in large partitioning dielectric radome. On the premise of guaranteeing mechanical performance of joint structure, the transmission efficiency of optimized mixed dielectric structure containing metallic wire grids improves by about 20% compared with plate joints. In addition, by loading different metallic wire grids, the frequency range of best transmission for mixed structure can be adjusted, thus can be used to develop radomes of various frequency. This provides a novel technological pathway to design high-performance large dielectric radomes.
2016, 33(6): 1311-1317.
doi: 10.13801/j.cnki.fhclxb.20160309.003
Abstract:
A model for angle-ply laminate Kirchhoff plate was developed based on the new modified couple stress theory. The new model contains only one scale parameter. The effects of ply angle on scale effect were analyzed. The principle of virtual work was employed to derive the bending equations and boundary conditions of laminate Kirchhoff plate in arbitrary ply angles. A simply supported antisymmetric microscale angle-ply laminate Kirchhoff plate was analytically solved by this new model. The results show that the scale effects of microscale anisotropic laminate not only depend on the characteristic size, but also depend on the ply angles. The ply angles may have significant effect on the scale effects.
A model for angle-ply laminate Kirchhoff plate was developed based on the new modified couple stress theory. The new model contains only one scale parameter. The effects of ply angle on scale effect were analyzed. The principle of virtual work was employed to derive the bending equations and boundary conditions of laminate Kirchhoff plate in arbitrary ply angles. A simply supported antisymmetric microscale angle-ply laminate Kirchhoff plate was analytically solved by this new model. The results show that the scale effects of microscale anisotropic laminate not only depend on the characteristic size, but also depend on the ply angles. The ply angles may have significant effect on the scale effects.
2016, 33(6): 1318-1326.
doi: 10.13801/j.cnki.fhclxb.20160308.002
Abstract:
Different winding strategies of composite winding based on robot can influence the winding craft and kinetic stability of the robot. In order to get better winding strategy of the robot kinetic stability, composite winding workstation of industrial robot with 6 degree of freedom was studied, in which individually analyze the influence of enveloping form, length of the hanging filament, geodesic and non-geodesic winding etc. on the robot kinetic stability and the variation parameters. MATLAB was used to calculate robot winding tracks in different winding strategies and determine winding track after projecting. Joint simulation of robot winding dynamics based on ADAMS and MATLAB was conducted to obtain curves of each joint torque of the robot, then the influence of the winding track after projecting on the robot kinetic stability of was analyzed. The experiment of dry fiber winding of composite products was carried out. The winding experiment indicates the optimized winding method adopts to stabilize the winding pattern and has no slip yarn, overlapping, overhead and other phenomena in the winding process, and the winding precision completely meets the design requirements.
Different winding strategies of composite winding based on robot can influence the winding craft and kinetic stability of the robot. In order to get better winding strategy of the robot kinetic stability, composite winding workstation of industrial robot with 6 degree of freedom was studied, in which individually analyze the influence of enveloping form, length of the hanging filament, geodesic and non-geodesic winding etc. on the robot kinetic stability and the variation parameters. MATLAB was used to calculate robot winding tracks in different winding strategies and determine winding track after projecting. Joint simulation of robot winding dynamics based on ADAMS and MATLAB was conducted to obtain curves of each joint torque of the robot, then the influence of the winding track after projecting on the robot kinetic stability of was analyzed. The experiment of dry fiber winding of composite products was carried out. The winding experiment indicates the optimized winding method adopts to stabilize the winding pattern and has no slip yarn, overlapping, overhead and other phenomena in the winding process, and the winding precision completely meets the design requirements.
