2016 Vol. 33, No. 1
2016, 33(1): 1-16.
doi: 10.13801/j.cnki.fhclxb.20151120.003
Abstract:
As key components of large composite structures, joints play important roles to ensure the integrity of composite structures. It is very difficult to analyze the strength and failure modes of composite joints due to their complex nonlinear coupling factors. Therefore, there is a need to monitor, diagnose, evaluate and predict the structure health state of composite joints. Information obtained through real-time monitoring will be used to determine the health condition of structures and the response to external loads, and further predict possible defects and failures that may occur in the future so that actions can be taken at the appropriate period of time to ensure the safety and service of composite structures to achieve maximum economic benefits. Taking the aerospace composite joints as examples, we first briefly analyzes the damages and failure modes of different composite joints, including bonded joint, mechanical joint and hybrid joints. Then the art of state of structural health monitoring (SHM) technology progess for composite joints is reviewed, including wave propagation method, impedance method, intelligent coating monitoring method, comparative vacuum monitoring method, fiber optical sensing monitoring method and hybrid integration approaches. Finally the development trend and the challenges of structural health monitoring of aircraft composite joint are discussed.
As key components of large composite structures, joints play important roles to ensure the integrity of composite structures. It is very difficult to analyze the strength and failure modes of composite joints due to their complex nonlinear coupling factors. Therefore, there is a need to monitor, diagnose, evaluate and predict the structure health state of composite joints. Information obtained through real-time monitoring will be used to determine the health condition of structures and the response to external loads, and further predict possible defects and failures that may occur in the future so that actions can be taken at the appropriate period of time to ensure the safety and service of composite structures to achieve maximum economic benefits. Taking the aerospace composite joints as examples, we first briefly analyzes the damages and failure modes of different composite joints, including bonded joint, mechanical joint and hybrid joints. Then the art of state of structural health monitoring (SHM) technology progess for composite joints is reviewed, including wave propagation method, impedance method, intelligent coating monitoring method, comparative vacuum monitoring method, fiber optical sensing monitoring method and hybrid integration approaches. Finally the development trend and the challenges of structural health monitoring of aircraft composite joint are discussed.
2016, 33(1): 17-26.
doi: 10.13801/j.cnki.fhclxb.20150331.002
Abstract:
Aiming to develop the process ability of liquid molding on two kinds of unidirectional fabric, compressibility and permeability tests were carried out on preform by two types of unidirectional fabric made of domestic CCF300 carbon fibers-plain unidirectional fabric U3160 and uniaxial non-crimp fabric KUC160. Two types of unidirectional fabric/bismaleimide resin composites were fabricated with resin transfer molding (RTM) processes, and in-plane mechanical properties of the composites were investigated and compared. It is found that the nesting effect during the preform compression test is influenced by the pressure and number of the fabric layers. The nesting effect is increased with the increase of pressure and the number of the layer. U3160 fabric displays more noticeable nesting effect than that of KUC160 fabric. Hence, the fiber volume fraction of KUC160 fabric preforms is about 20% lower than that of U3160 fabric preforms under high pressure. The permeability test results show that KUC160 has a higher permeability along the 0° direction than that of U3160 fabric, while the permeability perpendicular to the fibers of KUC160 fabric is lower than that of U3160 fabric. It may be attributed to that the binding effect of stitching yarns enhances the macro-flowing along the 0° direction, but weakens the micro-infiltration perpendicular to the fiber direction. In addition, the stitching yarns of KUC160 and the stabilizing yarns of U3160 have flow guiding effect on the permeability. Mechanical property test results show that compared with composites reinforced by U3160, the tensile, flexural and compressive properties along the 0° direction of KUC160 reinforced composites decrease. To be specific, tensile strength and flexural modulus decrease the most by 11% and 21%, respectively. The interlaminar shear strength slightly increases by about 8%.
Aiming to develop the process ability of liquid molding on two kinds of unidirectional fabric, compressibility and permeability tests were carried out on preform by two types of unidirectional fabric made of domestic CCF300 carbon fibers-plain unidirectional fabric U3160 and uniaxial non-crimp fabric KUC160. Two types of unidirectional fabric/bismaleimide resin composites were fabricated with resin transfer molding (RTM) processes, and in-plane mechanical properties of the composites were investigated and compared. It is found that the nesting effect during the preform compression test is influenced by the pressure and number of the fabric layers. The nesting effect is increased with the increase of pressure and the number of the layer. U3160 fabric displays more noticeable nesting effect than that of KUC160 fabric. Hence, the fiber volume fraction of KUC160 fabric preforms is about 20% lower than that of U3160 fabric preforms under high pressure. The permeability test results show that KUC160 has a higher permeability along the 0° direction than that of U3160 fabric, while the permeability perpendicular to the fibers of KUC160 fabric is lower than that of U3160 fabric. It may be attributed to that the binding effect of stitching yarns enhances the macro-flowing along the 0° direction, but weakens the micro-infiltration perpendicular to the fiber direction. In addition, the stitching yarns of KUC160 and the stabilizing yarns of U3160 have flow guiding effect on the permeability. Mechanical property test results show that compared with composites reinforced by U3160, the tensile, flexural and compressive properties along the 0° direction of KUC160 reinforced composites decrease. To be specific, tensile strength and flexural modulus decrease the most by 11% and 21%, respectively. The interlaminar shear strength slightly increases by about 8%.
2016, 33(1): 27-33.
doi: 10.13801/j.cnki.fhclxb.20150316.002
Abstract:
Na-montmorillonite (Na-MMT) which was modified by diphenyl methane-4,4'-diisocyanate (MDI) was exfoliated in nanoscale, MDI modified Na-MMT (M-MMT) was prepared. And then add M-MMT into monomer casting nylon 6 system to solve the thermal degradation problem that organic montmorillonite has presented in monomer casting nylon 6 system and improve the heat resisting property of the composites. The modification mechanism and dispersion of Na-MMT were investigated using FITR, GC-MS, XRD and TEM. Heat resisting, mechanical properties and the microstructure of M-MMT/monomer casting nylon 6 composites were investigated by TG, vicat softening, thermal deformation temperature test, mechanical property test and SEM observation. The results show that M-MMT is exfoliated by MDI, which is attributed to the reactions between MDI and the hydroxyl or the water in Na-MMT layers. In the monomer casting nylon 6 system, due to the mensurable initiator and those consumptions by MDI, the molecular mass of the M-MMT/monomer casting nylon 6 cmposites decreases, which leads to the declining mechanical properties, while the heat resisting of the cmposites improve because of the nanoscale effect of M-MMT. The vicat softening temperature increases up to 224℃, and the thermal deformation temperature increases up to 96℃, under loading condition of 1.82 MPa.
Na-montmorillonite (Na-MMT) which was modified by diphenyl methane-4,4'-diisocyanate (MDI) was exfoliated in nanoscale, MDI modified Na-MMT (M-MMT) was prepared. And then add M-MMT into monomer casting nylon 6 system to solve the thermal degradation problem that organic montmorillonite has presented in monomer casting nylon 6 system and improve the heat resisting property of the composites. The modification mechanism and dispersion of Na-MMT were investigated using FITR, GC-MS, XRD and TEM. Heat resisting, mechanical properties and the microstructure of M-MMT/monomer casting nylon 6 composites were investigated by TG, vicat softening, thermal deformation temperature test, mechanical property test and SEM observation. The results show that M-MMT is exfoliated by MDI, which is attributed to the reactions between MDI and the hydroxyl or the water in Na-MMT layers. In the monomer casting nylon 6 system, due to the mensurable initiator and those consumptions by MDI, the molecular mass of the M-MMT/monomer casting nylon 6 cmposites decreases, which leads to the declining mechanical properties, while the heat resisting of the cmposites improve because of the nanoscale effect of M-MMT. The vicat softening temperature increases up to 224℃, and the thermal deformation temperature increases up to 96℃, under loading condition of 1.82 MPa.
2016, 33(1): 34-43.
doi: 10.13801/j.cnki.fhclxb.20150518.003
Abstract:
The graphene oxide was reduced by hydrazine hydrate to attain two kinds of reduced graphene oxide (rGO) with different oxygen contents. The prepreg was prepared from carbon fiber (CF) and bismaleimide (BMI) resin by wet impregnating process, then the rGO-CF/BMI composite unidirectional laminates were manufactured by hot pressing process. The relationship between reduced degree and content of rGO and mechanical properties, glass transition temperature and electromagnetic properties of composites was studied. The results show that the reduced degree of rGO2 which was attained under the higher temperature is larger than that of rGO1 which was attained under the lower temperature, the dispersion of rGO2 is poorer than rGO1 in resin. The interlaminar shear strength of rGO1-CF/BMI and rGO2-CF/BMI composites will both be enhanced about 14% compared to CF/BMI composites when the mass fraction of rGO1 and rGO2 is 0.1% and 0.05% respectively, however, the flexural properties and glass transition temperature are basically unchanged. The dielectric properties of rGO2-CF/BMI composites are superior to those of rGO1-CF/BMI composites. When the mass fraction of rGO2 is 0.1%, the real part dielectric constants of rGO2-CF/BMI composites will increase by over 6 times than those of CF/BMI composites, as well as the dielectric losses will increase by over 3 times at the frequency range of 12.4-18.0 GHz. Moreover, the magnetic properties of rGO1-CF/BMI and rGO2-CF/BMI composites are pretty weak, thus the interaction between the composites and electromagnetic wave is mainly reflection, rather than absorption.
The graphene oxide was reduced by hydrazine hydrate to attain two kinds of reduced graphene oxide (rGO) with different oxygen contents. The prepreg was prepared from carbon fiber (CF) and bismaleimide (BMI) resin by wet impregnating process, then the rGO-CF/BMI composite unidirectional laminates were manufactured by hot pressing process. The relationship between reduced degree and content of rGO and mechanical properties, glass transition temperature and electromagnetic properties of composites was studied. The results show that the reduced degree of rGO2 which was attained under the higher temperature is larger than that of rGO1 which was attained under the lower temperature, the dispersion of rGO2 is poorer than rGO1 in resin. The interlaminar shear strength of rGO1-CF/BMI and rGO2-CF/BMI composites will both be enhanced about 14% compared to CF/BMI composites when the mass fraction of rGO1 and rGO2 is 0.1% and 0.05% respectively, however, the flexural properties and glass transition temperature are basically unchanged. The dielectric properties of rGO2-CF/BMI composites are superior to those of rGO1-CF/BMI composites. When the mass fraction of rGO2 is 0.1%, the real part dielectric constants of rGO2-CF/BMI composites will increase by over 6 times than those of CF/BMI composites, as well as the dielectric losses will increase by over 3 times at the frequency range of 12.4-18.0 GHz. Moreover, the magnetic properties of rGO1-CF/BMI and rGO2-CF/BMI composites are pretty weak, thus the interaction between the composites and electromagnetic wave is mainly reflection, rather than absorption.
2016, 33(1): 44-52.
doi: 10.13801/j.cnki.fhclxb.20150410.004
Abstract:
Based on carbon nanotubes (CNTs) film prepared by floating catalyst chemical vapor deposition (CVD) method, the component of amorphous substance coating on CNTs surface was firstly analyzed by infrared spectroscopy. Moreover, heat-treatment and acid-treatment were used separately to investigate the effects of amorphous substance and residual Fe catalyst in CNTs film on tensile orientation behavior of CNTs film. The results indicate that the amorphous substances on surface of CNTs in CNTs film prepared by CVD method are oligomer containing oxygen, alkane or olefin groups, which can be removed through 350℃ treatment in air. The component of CNTs film can significantly impact the aligning and rearranging behavior of CNTs film. The oligomer on surface of CNTs film tends to enhance the interaction between CNTs and Fe catalyst particle serves as crossing junctions of the CNTs network, which both improve the CNTs orientation degree and the size of bundles, and hence increase the tensile stability and breakage toughness of the CNTs film. After stretching, the CNTs film has better wettability with epoxy solution, and the tensile strength and modulus of CNTs film/epoxy composites reach 1 228 MPa and 94.5 GPa respectively, which are increased by 337% and 729% than the initial random CNTs film/epoxy composites.
Based on carbon nanotubes (CNTs) film prepared by floating catalyst chemical vapor deposition (CVD) method, the component of amorphous substance coating on CNTs surface was firstly analyzed by infrared spectroscopy. Moreover, heat-treatment and acid-treatment were used separately to investigate the effects of amorphous substance and residual Fe catalyst in CNTs film on tensile orientation behavior of CNTs film. The results indicate that the amorphous substances on surface of CNTs in CNTs film prepared by CVD method are oligomer containing oxygen, alkane or olefin groups, which can be removed through 350℃ treatment in air. The component of CNTs film can significantly impact the aligning and rearranging behavior of CNTs film. The oligomer on surface of CNTs film tends to enhance the interaction between CNTs and Fe catalyst particle serves as crossing junctions of the CNTs network, which both improve the CNTs orientation degree and the size of bundles, and hence increase the tensile stability and breakage toughness of the CNTs film. After stretching, the CNTs film has better wettability with epoxy solution, and the tensile strength and modulus of CNTs film/epoxy composites reach 1 228 MPa and 94.5 GPa respectively, which are increased by 337% and 729% than the initial random CNTs film/epoxy composites.
2016, 33(1): 53-60.
doi: 10.13801/j.cnki.fhclxb.20150325.003
Abstract:
In order to investigate the effects of graphene oxide (GO) on the mechanical properties of polymer matrix composites, GO/poly (vinyl alcohol) (PVA) composites were prepared by solution mixing method firstly. Then, the structure, interfacial bonding properties, mechanical properties, creep behaviors and water swelling rate of GO/PVA composites were investigate by XRD, TEM, FTIR, DSC, nanoindentation and so on. The results show that GO can be dispersed well in the PVA matrix, both of them are mainly combined through hydrogen bond interaction which has higher interface bonding force. Comparing with that of pure PVA, the hardness and effective elastic modulus of 1wt% GO/PVA composite enhance by 28.9% and 23.3%, respectively, and the indentation creep depth declines by 19.8%. GO/PVA composites show the lower ratios of infinite shear modulus to instantaneous shear modulus, which indicates that GO improves the creep resistance of PVA. The addition of GO also improves the waterproofness of GO/PVA composites and decreases swelling factor. The experimental results of moisture absorption nanoindentation show that the mechanical properties of pure PVA decline with the moisture absorption time increasing, while the mechanical properties of GO/PVA composite almost remain the same after moisture absorption for 72 h. The obtained conclusions provide theoretic guidance for the research of graphene reinforced polymer matrix composites.
In order to investigate the effects of graphene oxide (GO) on the mechanical properties of polymer matrix composites, GO/poly (vinyl alcohol) (PVA) composites were prepared by solution mixing method firstly. Then, the structure, interfacial bonding properties, mechanical properties, creep behaviors and water swelling rate of GO/PVA composites were investigate by XRD, TEM, FTIR, DSC, nanoindentation and so on. The results show that GO can be dispersed well in the PVA matrix, both of them are mainly combined through hydrogen bond interaction which has higher interface bonding force. Comparing with that of pure PVA, the hardness and effective elastic modulus of 1wt% GO/PVA composite enhance by 28.9% and 23.3%, respectively, and the indentation creep depth declines by 19.8%. GO/PVA composites show the lower ratios of infinite shear modulus to instantaneous shear modulus, which indicates that GO improves the creep resistance of PVA. The addition of GO also improves the waterproofness of GO/PVA composites and decreases swelling factor. The experimental results of moisture absorption nanoindentation show that the mechanical properties of pure PVA decline with the moisture absorption time increasing, while the mechanical properties of GO/PVA composite almost remain the same after moisture absorption for 72 h. The obtained conclusions provide theoretic guidance for the research of graphene reinforced polymer matrix composites.
2016, 33(1): 61-70.
doi: 10.13801/j.cnki.fhclxb.20150518.001
Abstract:
In order to prepare the polylactic acid (PLA) composites with excellent strength and toughness, octa (propylglycidyl ether) polyhedral oligomeric silsesquioxane (Ope-POSS) nano particles were added into PLA, and PLA grafted by glycidyl methacrylate (PLA-g-GMA) was added as compatibilization and toughening component firstly. Then, PLA-g-GMA/Ope-POSS/PLA composites were prepared by melt blending method. Finally, by the characterization of morphological structure, thermal properties, mechanical properties and hydrophobicity of the composites, the effects of the addition of Ope-POSS nano particles and PLA-g-GMA on the properties of the PLA composites were analyzed. The results show that the addition of PLA-g-GMA plays an effective compatibilizing effect for Ope-POSS nano particles, resulting in the better dispersion of Ope-POSS nano particles in the composites. With the amount of well dispersed Ope-POSS nano particles increasing, the strength, thermostability and hydrophobicity of PLA composites are all improved significantly, and the toughness is also advanced with PLA-g-GMA content increasing. When the PLA-g-GMA and Ope-POSS nano particle contents are 4wt% and 3wt% of PLA respectively, the properties of PLA-g-GMA/Ope-POSS/PLA composite are optimal. The obtained conclusions provide theoretical guidance for the further investigation of POSS hybridized PLA composites.
In order to prepare the polylactic acid (PLA) composites with excellent strength and toughness, octa (propylglycidyl ether) polyhedral oligomeric silsesquioxane (Ope-POSS) nano particles were added into PLA, and PLA grafted by glycidyl methacrylate (PLA-g-GMA) was added as compatibilization and toughening component firstly. Then, PLA-g-GMA/Ope-POSS/PLA composites were prepared by melt blending method. Finally, by the characterization of morphological structure, thermal properties, mechanical properties and hydrophobicity of the composites, the effects of the addition of Ope-POSS nano particles and PLA-g-GMA on the properties of the PLA composites were analyzed. The results show that the addition of PLA-g-GMA plays an effective compatibilizing effect for Ope-POSS nano particles, resulting in the better dispersion of Ope-POSS nano particles in the composites. With the amount of well dispersed Ope-POSS nano particles increasing, the strength, thermostability and hydrophobicity of PLA composites are all improved significantly, and the toughness is also advanced with PLA-g-GMA content increasing. When the PLA-g-GMA and Ope-POSS nano particle contents are 4wt% and 3wt% of PLA respectively, the properties of PLA-g-GMA/Ope-POSS/PLA composite are optimal. The obtained conclusions provide theoretical guidance for the further investigation of POSS hybridized PLA composites.
2016, 33(1): 71-76.
doi: 10.13801/j.cnki.fhclxb.20150522.004
Abstract:
Non-uniformity of curing degree fields during curing process of composites is an important factor in causing residual thermal stress and curing shrinkage stress. In order to investigate the influences of process parameters on the curing uniformity during the curing molding process of resin matrix composite structures, a composite curing simulation model was built for Epon 862/W epoxy system firstly, and the model was verified. Then, the dimensionless form of heat transfer equation and curing kinetics equation about resin matrix composite structures was obtained by dimensional analysis. Finally, the influence rules of curing process temperature, convective heat transfer coefficient and thickness of the structure on curing uniformity of the composites were quantitatively analyzed by numerical simulation. The results show that the convective heat transfer coefficient has little effect on curing uniformity of composites under the condition of isothermal curing. There is a fitting function relationship between the dimensionless group characteristic time tc/characteristic resin curing reaction time tR and the difference of curing degree, and the function can be used in engineering calculation conveniently.
Non-uniformity of curing degree fields during curing process of composites is an important factor in causing residual thermal stress and curing shrinkage stress. In order to investigate the influences of process parameters on the curing uniformity during the curing molding process of resin matrix composite structures, a composite curing simulation model was built for Epon 862/W epoxy system firstly, and the model was verified. Then, the dimensionless form of heat transfer equation and curing kinetics equation about resin matrix composite structures was obtained by dimensional analysis. Finally, the influence rules of curing process temperature, convective heat transfer coefficient and thickness of the structure on curing uniformity of the composites were quantitatively analyzed by numerical simulation. The results show that the convective heat transfer coefficient has little effect on curing uniformity of composites under the condition of isothermal curing. There is a fitting function relationship between the dimensionless group characteristic time tc/characteristic resin curing reaction time tR and the difference of curing degree, and the function can be used in engineering calculation conveniently.
2016, 33(1): 77-83.
doi: 10.13801/j.cnki.fhclxb.20150716.001
Abstract:
Using styrene (St) as monomer and organic silicone resin with methacryloxypropyl group (MTQ) as crosslinking-agent, the MTQ/polystyrene (PS) porous composites with honeycomb, low densities and high porosity were prepared by high internal phase ratio emulsions template (HIPE) method. The effects of MTQ on microstructure, compressive properties and thermal stability of polymer porous composites were investigated. Results indicate that the MTQ/PS porous composites have three-dimensional spherical cavities and rich interconnection pores in cavities wall, connectivity is good, and the diameters of pores range from 2-9 μm with the average interconnection pores diameters of 0.35-1.85 μm. The porosity of porous materials could be controlled, and total porosity could reach as high as 92%. Additionally, the compressive strength of porous composites is 0.28-0.74 MPa, and compressive modulus is 4.86-13.54 MPa. When the MTQ to St mass ratio is 30:100, MTQ/PS porous composites with smaller cavities diameter, narrow interconnection pores, good compression properties and thermal stability could be obtained.
Using styrene (St) as monomer and organic silicone resin with methacryloxypropyl group (MTQ) as crosslinking-agent, the MTQ/polystyrene (PS) porous composites with honeycomb, low densities and high porosity were prepared by high internal phase ratio emulsions template (HIPE) method. The effects of MTQ on microstructure, compressive properties and thermal stability of polymer porous composites were investigated. Results indicate that the MTQ/PS porous composites have three-dimensional spherical cavities and rich interconnection pores in cavities wall, connectivity is good, and the diameters of pores range from 2-9 μm with the average interconnection pores diameters of 0.35-1.85 μm. The porosity of porous materials could be controlled, and total porosity could reach as high as 92%. Additionally, the compressive strength of porous composites is 0.28-0.74 MPa, and compressive modulus is 4.86-13.54 MPa. When the MTQ to St mass ratio is 30:100, MTQ/PS porous composites with smaller cavities diameter, narrow interconnection pores, good compression properties and thermal stability could be obtained.
2016, 33(1): 84-91.
doi: 10.13801/j.cnki.fhclxb.20150518.004
Abstract:
The polystyrene (PS) microspheres which were prepared by dispersion polymerization method were served as a template, the precursor PS-Gd (OH) CO3 composite microspheres were prepared by homogeneous precipitation technique. The Gd2O3 hollow microspheres were obtained after the polymer microsphere templates were removed through calcinations. Low frequency and high damping Gd2O3/butyl rubber composites were prepared by blending Gd2O3 hollow microspheres with butyl rubber. FTIR, SEM, TEM, TG analysis, XRD and XPS were employed to characterize the structure and morphology of the Gd2O3 hollow microspheres. Gd2O3/butyl rubber composites were prepared by adding Gd2O3 hollow microspheres and powder as fillers to the butyl rubber separately. The results show that Gd2O3 hollow microspheres were composed of cubic fluorite structure with 0.9 μm outer diameter and about 100 nm shell thickness. The damping properties of composite with Gd2O3 hollow microspheres are better than that with Gd2O3 powder. Low frequency damping property of Gd2O3/butyl rubber composite has improved significantly compared with that of pure butyl rubber.
The polystyrene (PS) microspheres which were prepared by dispersion polymerization method were served as a template, the precursor PS-Gd (OH) CO3 composite microspheres were prepared by homogeneous precipitation technique. The Gd2O3 hollow microspheres were obtained after the polymer microsphere templates were removed through calcinations. Low frequency and high damping Gd2O3/butyl rubber composites were prepared by blending Gd2O3 hollow microspheres with butyl rubber. FTIR, SEM, TEM, TG analysis, XRD and XPS were employed to characterize the structure and morphology of the Gd2O3 hollow microspheres. Gd2O3/butyl rubber composites were prepared by adding Gd2O3 hollow microspheres and powder as fillers to the butyl rubber separately. The results show that Gd2O3 hollow microspheres were composed of cubic fluorite structure with 0.9 μm outer diameter and about 100 nm shell thickness. The damping properties of composite with Gd2O3 hollow microspheres are better than that with Gd2O3 powder. Low frequency damping property of Gd2O3/butyl rubber composite has improved significantly compared with that of pure butyl rubber.
2016, 33(1): 92-99.
doi: 10.13801/j.cnki.fhclxb.20150522.001
Abstract:
Blend proton exchange membrane with polyhedral oligomeric silsesquioxane (POSS) star topological structure block copolymer graphene oxide (GO)/polyhedral oligomeric silsesquioxane-(polymethylmethacrylate-block-polystyrene)(POSS-(PMMA26-b-SPS156)8) was prepared by the blending method. The effects of GO content on the properties of blend proton exchange membrane were investigated by testing ion exchange capacity (IEC), proton conductivity, water uptake and swelling rate. It is found that the ion exchange capacity of the blend proton exchange membrane increases with the increase of GO content, while water uptake and swelling rate reduce with adding GO. The blend proton exchange membrane shows higher dimensional stability in the determination of temperature range. The decline of the conductivity of pure polymer membranes owing to water loss in 80℃ can be improved by adding GO. The proton conductivity of proton exchange membrane can be improved, It is found that the proton conductivity of the blend proton exchange membrane with 0.3wt% content of GO is approximately 3.2 times bigger than that of the pure polymer membranes in 100% relative humidity at 80℃.
Blend proton exchange membrane with polyhedral oligomeric silsesquioxane (POSS) star topological structure block copolymer graphene oxide (GO)/polyhedral oligomeric silsesquioxane-(polymethylmethacrylate-block-polystyrene)(POSS-(PMMA26-b-SPS156)8) was prepared by the blending method. The effects of GO content on the properties of blend proton exchange membrane were investigated by testing ion exchange capacity (IEC), proton conductivity, water uptake and swelling rate. It is found that the ion exchange capacity of the blend proton exchange membrane increases with the increase of GO content, while water uptake and swelling rate reduce with adding GO. The blend proton exchange membrane shows higher dimensional stability in the determination of temperature range. The decline of the conductivity of pure polymer membranes owing to water loss in 80℃ can be improved by adding GO. The proton conductivity of proton exchange membrane can be improved, It is found that the proton conductivity of the blend proton exchange membrane with 0.3wt% content of GO is approximately 3.2 times bigger than that of the pure polymer membranes in 100% relative humidity at 80℃.
2016, 33(1): 100-106.
doi: 10.13801/j.cnki.fhclxb.20150609.002
Abstract:
In order to prepare the shielding materials of the rare-earth type which has light weight and unleaded innocuity, maleic acid samarium complex (Sm-MA) was synthesized by Sm2O3 and maleic anhydride (MA) through precipitation method firstly. Then, Sm-MA was used to modify ethylene propylene diene monomer rubber (EPDM), and Sm-MA/EPDM composites were prepared. Finally, the Sm-MA was tested by TG, FTIR, SEM and XRD, as well as the mechanical properties, morphology and shielding property (X-ray energy was 59.3 keV) of Sm-MA/EPDM composites were characterized respectively. The TG results show that the thermal decomposition mass loss of Sm-MA is closed to end at about 850℃, the total mass loss ratio of Sm-MA is 43.7%, and the content of Sm in Sm-MA (47.6wt%) which is calculated by experimental data is approximately consistent with the theoretical calculated value 46.8wt%. The FTIR spectra show that the characteristics absorption peak of -COOH in MA disappears after the formation of complex, as well as symmetrical and antisymmetric stretching vibration absorption peaks of carboxylic acid appear, which means Sm3+and MA bonded. Mechanical property and shielding property test results show that Sm-MA can reinforce both of the mechanical properties and shielding property of EPDM significantly. When the mass ratio of Sm-MA to EPDM is 60:100, the properties of Sm-MA/EPDM composites reach the best, the tensile strength is 18.3 MPa, the reinforced ratio reaches 33.6% and the shielding ratio reaches 77.1%. The conclusions obtained indicate that the addition of innocuity metal complex can not only improve the properties of composites, but also enhances the compatibility with environment.
In order to prepare the shielding materials of the rare-earth type which has light weight and unleaded innocuity, maleic acid samarium complex (Sm-MA) was synthesized by Sm2O3 and maleic anhydride (MA) through precipitation method firstly. Then, Sm-MA was used to modify ethylene propylene diene monomer rubber (EPDM), and Sm-MA/EPDM composites were prepared. Finally, the Sm-MA was tested by TG, FTIR, SEM and XRD, as well as the mechanical properties, morphology and shielding property (X-ray energy was 59.3 keV) of Sm-MA/EPDM composites were characterized respectively. The TG results show that the thermal decomposition mass loss of Sm-MA is closed to end at about 850℃, the total mass loss ratio of Sm-MA is 43.7%, and the content of Sm in Sm-MA (47.6wt%) which is calculated by experimental data is approximately consistent with the theoretical calculated value 46.8wt%. The FTIR spectra show that the characteristics absorption peak of -COOH in MA disappears after the formation of complex, as well as symmetrical and antisymmetric stretching vibration absorption peaks of carboxylic acid appear, which means Sm3+and MA bonded. Mechanical property and shielding property test results show that Sm-MA can reinforce both of the mechanical properties and shielding property of EPDM significantly. When the mass ratio of Sm-MA to EPDM is 60:100, the properties of Sm-MA/EPDM composites reach the best, the tensile strength is 18.3 MPa, the reinforced ratio reaches 33.6% and the shielding ratio reaches 77.1%. The conclusions obtained indicate that the addition of innocuity metal complex can not only improve the properties of composites, but also enhances the compatibility with environment.
2016, 33(1): 107-115.
doi: 10.13801/j.cnki.fhclxb.20150417.003
Abstract:
Silicone rubber core mold is one of the key tooling to realize the co-curing molding process of resin matrix thermosetting composite hat-stiffened structures, while in the curing and heating process of prepreg, the heat inflation of silicone rubber core mold needs to be eliminated by prefabricating appropriate adjusting hole, so as to ensure the forming quality of hat-stiffened structure. The silicone rubber core molds with different structures were simulated using computer by establishing the thermo-mechanical coupled finite element analysis model for the prefabricated adjusting hole of silicone rubber core mold, thus the optimal size range of the prefabricated adjusting hole of silicone rubber mold which can realize the collaborative manufacture of shape and properties of composite hat-stiffened structures' was obtained firstly. Then, the possible impact factors of heating expansion of silicone rubber core mold were analyzed comprehensively, so that the calculation model of prefabricated adjusting hole considering the volume correction coefficient was found. After that, the volume correction coefficient for the prefabricated adjusting hole of core mold was regressed by finite element method, and the regressed correction coefficient was employed to conduct the simulation verification of the hat-stiffened structures with different sizes of cross-sections. Thus, the relative accurate theoretical calculating model for prefabricated adjusting hole was determined. Finally, the correctness of the mathematical model and the finite element analysis was verified by experiments, which would provide theory and experimental basis for the fabrication of composite hat-stiffened structures.
Silicone rubber core mold is one of the key tooling to realize the co-curing molding process of resin matrix thermosetting composite hat-stiffened structures, while in the curing and heating process of prepreg, the heat inflation of silicone rubber core mold needs to be eliminated by prefabricating appropriate adjusting hole, so as to ensure the forming quality of hat-stiffened structure. The silicone rubber core molds with different structures were simulated using computer by establishing the thermo-mechanical coupled finite element analysis model for the prefabricated adjusting hole of silicone rubber core mold, thus the optimal size range of the prefabricated adjusting hole of silicone rubber mold which can realize the collaborative manufacture of shape and properties of composite hat-stiffened structures' was obtained firstly. Then, the possible impact factors of heating expansion of silicone rubber core mold were analyzed comprehensively, so that the calculation model of prefabricated adjusting hole considering the volume correction coefficient was found. After that, the volume correction coefficient for the prefabricated adjusting hole of core mold was regressed by finite element method, and the regressed correction coefficient was employed to conduct the simulation verification of the hat-stiffened structures with different sizes of cross-sections. Thus, the relative accurate theoretical calculating model for prefabricated adjusting hole was determined. Finally, the correctness of the mathematical model and the finite element analysis was verified by experiments, which would provide theory and experimental basis for the fabrication of composite hat-stiffened structures.
2016, 33(1): 116-122.
doi: 10.13801/j.cnki.fhclxb.20150522.006
Abstract:
In order to promote the engineering application of polyvinyl alcohol (PVA) fiber reinforced engineered cementitious composites (PVA-ECC) in thermal environment, mechanical property change of PVA-ECC with high-volume of fly ash after thermal treatment was investigated through dogbone specimen tensile test. The single fiber tensile test, single fiber pullout test and single crack tensile test were conducted to explore the performance improvement mechanism of PVA-ECC. The results indicate that PVA-ECC can keep its characteristic of multiple-cracking after thermal treatment by no more than 200℃. Compared to 20℃, tensile mechanical properties are significantly improved after being treated at 50, 100, 200℃, and the rule is: 100℃> 50℃> 200℃.The fiber strength is not a controlled factor for the change of PVA-ECC tensile properties, and a proper thermal treatment enhances chemical bond and frictional bond between fiber and matrix, and thus increases bridge stress and crack complementary energy, which result in the improvements of tensile properties and friction energy dissipation capacity for PVA-ECC. The mechanism analysis of PVA-ECC performance variation provides a sound theoretical basis for PVA-ECC engineering design.
In order to promote the engineering application of polyvinyl alcohol (PVA) fiber reinforced engineered cementitious composites (PVA-ECC) in thermal environment, mechanical property change of PVA-ECC with high-volume of fly ash after thermal treatment was investigated through dogbone specimen tensile test. The single fiber tensile test, single fiber pullout test and single crack tensile test were conducted to explore the performance improvement mechanism of PVA-ECC. The results indicate that PVA-ECC can keep its characteristic of multiple-cracking after thermal treatment by no more than 200℃. Compared to 20℃, tensile mechanical properties are significantly improved after being treated at 50, 100, 200℃, and the rule is: 100℃> 50℃> 200℃.The fiber strength is not a controlled factor for the change of PVA-ECC tensile properties, and a proper thermal treatment enhances chemical bond and frictional bond between fiber and matrix, and thus increases bridge stress and crack complementary energy, which result in the improvements of tensile properties and friction energy dissipation capacity for PVA-ECC. The mechanism analysis of PVA-ECC performance variation provides a sound theoretical basis for PVA-ECC engineering design.
2016, 33(1): 123-131.
doi: 10.13801/j.cnki.fhclxb.20150407.001
Abstract:
In order to investigate the preparation method and photocatalytic properties of composites comprised by reduced graphene oxide (RGO) and TiO2 with high activity facets, RGO/nano TiO2 composites were prepared by two-step hydrothermal method: the 1st step was the synthesis of nano TiO2 exposed with high activity facets; the 2nd step was the recombination of as-synthesized nano TiO2 and graphene oxide (GO), thus RGO/nano TiO2 composites were formed. Then, the prepared nano TiO2 with different exposed facets and RGO/nano TiO2 composites were characterized by means of XRD, SEM, X-ray photoelectron spectrometer, ultraviolet-visible diffuse reflectance spectroscopy and so on, and the photocatalytic properties were evaluated. The results show that during the 1st step of hydrothermal method, nano TiO2 which has high activity (001) and (101) facets can be controllably prepared by adjusting the concentration of HF. Fluorine atoms exist in nano TiO2 by two states of physically adsorbing state and chemically binding state. After the 2nd step, GO recombines with nano TiO2 to form RGO/nano TiO2 composite, and GO is transformed to RGO simultaneously in the process. RGO/nano TiO2 composites synthesized by two-step hydrothermal method have favorable photocatalytic performances under ultraviolet illumination, which outperform those of commercial TiO2 (P25) and nano TiO2. The photocatalytic properties of RGO/nano TiO2 composites have remarkable improvement. RGO and exposed facets of TiO2 have effects on the photocatalytic activity.
In order to investigate the preparation method and photocatalytic properties of composites comprised by reduced graphene oxide (RGO) and TiO2 with high activity facets, RGO/nano TiO2 composites were prepared by two-step hydrothermal method: the 1st step was the synthesis of nano TiO2 exposed with high activity facets; the 2nd step was the recombination of as-synthesized nano TiO2 and graphene oxide (GO), thus RGO/nano TiO2 composites were formed. Then, the prepared nano TiO2 with different exposed facets and RGO/nano TiO2 composites were characterized by means of XRD, SEM, X-ray photoelectron spectrometer, ultraviolet-visible diffuse reflectance spectroscopy and so on, and the photocatalytic properties were evaluated. The results show that during the 1st step of hydrothermal method, nano TiO2 which has high activity (001) and (101) facets can be controllably prepared by adjusting the concentration of HF. Fluorine atoms exist in nano TiO2 by two states of physically adsorbing state and chemically binding state. After the 2nd step, GO recombines with nano TiO2 to form RGO/nano TiO2 composite, and GO is transformed to RGO simultaneously in the process. RGO/nano TiO2 composites synthesized by two-step hydrothermal method have favorable photocatalytic performances under ultraviolet illumination, which outperform those of commercial TiO2 (P25) and nano TiO2. The photocatalytic properties of RGO/nano TiO2 composites have remarkable improvement. RGO and exposed facets of TiO2 have effects on the photocatalytic activity.
2016, 33(1): 132-141.
doi: 10.13801/j.cnki.fhclxb.20150410.005
Abstract:
In order to realize the recycling utilization of Pisha sandstone, Pisha sandstone was transformed to modified steel slag/Pisha sandstone composites which had good mechanical properties by alkali-activated method and mixing with suitable amount of steel slag. Then, the effects of dosages of steel slag, alkali-activator and age on compressive strength and softening coefficients of modified steel slag/Pisha sandstone composites were investigated systematacially. Finally, SEM/EDS, FTIR and XRD were used to analyze the hydration process and carbonation process of modified steel slag/Pisha sandstone composites. The results show that the 90 d compressive strength and softening coefficient of modified steel slag/Pisha sandstone composites achieve 46.0 MPa and 0.94 respectively, which fully meet the requirements of engineering application. The main hydration products of modified steel slag/Pisha sandstone composites are C-S-H gel and geopolymer gel, and C-S-H gel has relatively serious carbonation phenomena. When the dosages of steel slag and NaOH are 20.0wt% and 1.5wt% respectively, the 28 d carbonation rate of C-S-H gel reaches 30.1%, and carbonation rate decreases with the dosages of steel slag and NaOH increasing, but carbonation rate has little effect on strength. Modified steel slag/Pisha sandstone composites have good mechanical properties and water resistance.
In order to realize the recycling utilization of Pisha sandstone, Pisha sandstone was transformed to modified steel slag/Pisha sandstone composites which had good mechanical properties by alkali-activated method and mixing with suitable amount of steel slag. Then, the effects of dosages of steel slag, alkali-activator and age on compressive strength and softening coefficients of modified steel slag/Pisha sandstone composites were investigated systematacially. Finally, SEM/EDS, FTIR and XRD were used to analyze the hydration process and carbonation process of modified steel slag/Pisha sandstone composites. The results show that the 90 d compressive strength and softening coefficient of modified steel slag/Pisha sandstone composites achieve 46.0 MPa and 0.94 respectively, which fully meet the requirements of engineering application. The main hydration products of modified steel slag/Pisha sandstone composites are C-S-H gel and geopolymer gel, and C-S-H gel has relatively serious carbonation phenomena. When the dosages of steel slag and NaOH are 20.0wt% and 1.5wt% respectively, the 28 d carbonation rate of C-S-H gel reaches 30.1%, and carbonation rate decreases with the dosages of steel slag and NaOH increasing, but carbonation rate has little effect on strength. Modified steel slag/Pisha sandstone composites have good mechanical properties and water resistance.
2016, 33(1): 142-148.
doi: 10.13801/j.cnki.fhclxb.20150522.005
Abstract:
Using the titanium tetrachloride as raw material, nano-TiO2 compound membrane was synthesized by the hydrolysis precipitation method. The crystal structure, morphology of TiO2/diatomite-based porous ceramics were characterized by XRD, TEM, FTIR and so on. Composite as the air filter core body, the photocatalytic kinetics of materials was investigated by the degradation for formaldehyde. The results indicate that nano-TiO2 calcined at 600℃ is anatase, and the average grain size of TiO2 is 10.6 nm. Nano-TiO2 thin film is loaded strongly on the carrier surface, and the thickness is 300-450 nm. The Si-O-Ti bonds between the interface of the coating layer and the surface of nano-TiO2 particle are formed. The elimination ratio of the composites for formaldehyde with the concentration 1.302 mg/m3 reaches 94.6% in 240 min under an ultraviolet lamp irradiation. Kinetics study showed that the kinetics of formaldehyde degradation inaction can be described by Langmuir-Hinshelwood model. The rate constant of the gas phase photocatalytic first order reaction and adsorption coefficient are 0.576 mg/(m3·min) and 0.048 m3/mg respectively. The kinetic equations of photocatalysis are established.
Using the titanium tetrachloride as raw material, nano-TiO2 compound membrane was synthesized by the hydrolysis precipitation method. The crystal structure, morphology of TiO2/diatomite-based porous ceramics were characterized by XRD, TEM, FTIR and so on. Composite as the air filter core body, the photocatalytic kinetics of materials was investigated by the degradation for formaldehyde. The results indicate that nano-TiO2 calcined at 600℃ is anatase, and the average grain size of TiO2 is 10.6 nm. Nano-TiO2 thin film is loaded strongly on the carrier surface, and the thickness is 300-450 nm. The Si-O-Ti bonds between the interface of the coating layer and the surface of nano-TiO2 particle are formed. The elimination ratio of the composites for formaldehyde with the concentration 1.302 mg/m3 reaches 94.6% in 240 min under an ultraviolet lamp irradiation. Kinetics study showed that the kinetics of formaldehyde degradation inaction can be described by Langmuir-Hinshelwood model. The rate constant of the gas phase photocatalytic first order reaction and adsorption coefficient are 0.576 mg/(m3·min) and 0.048 m3/mg respectively. The kinetic equations of photocatalysis are established.
2016, 33(1): 149-154.
doi: 10.13801/j.cnki.fhclxb.20150417.005
Abstract:
In order to study the failure mechanism under low cycle fatigue loading of ceramic matrix composites, their fatigue behavior was investigated through tests and mesoscopre analysis. The effects of loading cycles on the residual strength after tension-tension fatigue were studied for 2D needled C/SiC composites at room temperature. The fracture morphology and microstructure of the materials were observed by optical microscope and scanning electron microscope. The results show that the 2D needled C/SiC composites present an outstanding fatigue resistance as the loading cycle is over 106 cycles while loading at level of 85% ultimate tensile strength (UTS). With the increase of loading cycles, the residual strength first increases then declines. The fracture analysis shows that the length of pull-out fibers increases as loading cycle increase, which means that in the process of fatigue loading, the bonding strength of fiber/matrix interface declines, which can eliminate the stress nonuniformity in materials and enhance the bearing capacity of the composites, and result in the fatigue strengthening phenomenon of 2D needled C/SiC composites.
In order to study the failure mechanism under low cycle fatigue loading of ceramic matrix composites, their fatigue behavior was investigated through tests and mesoscopre analysis. The effects of loading cycles on the residual strength after tension-tension fatigue were studied for 2D needled C/SiC composites at room temperature. The fracture morphology and microstructure of the materials were observed by optical microscope and scanning electron microscope. The results show that the 2D needled C/SiC composites present an outstanding fatigue resistance as the loading cycle is over 106 cycles while loading at level of 85% ultimate tensile strength (UTS). With the increase of loading cycles, the residual strength first increases then declines. The fracture analysis shows that the length of pull-out fibers increases as loading cycle increase, which means that in the process of fatigue loading, the bonding strength of fiber/matrix interface declines, which can eliminate the stress nonuniformity in materials and enhance the bearing capacity of the composites, and result in the fatigue strengthening phenomenon of 2D needled C/SiC composites.
2016, 33(1): 155-162.
doi: 10.13801/j.cnki.fhclxb.20150428.003
Abstract:
In order to explore the method of using ultraviolet light and coupled thermal reduction process to prepare RGO/nanoTiO2 composites under the assistance of ultrasonic and investigate the photocatalytic reduction performance in the anoxic water, graphene oxide (GO) was prepared by improved Hummers method using flake graphite as raw material, and reduced graphene oxide (RGO) was prepared by ultrasonic/ultraviolet light reduction process firstly. Then, butyl titanate ester and RGO were used as precursors, RGO/nanoTiO2 composite photocatalytic materials were prepared by the method of sol-gel and high temperature heating under nitrogen protection. After that, the structure and properties of RGO/nanoTiO2 composites were characterized by FTIR, XRD, BET and ultraviolet-visible spectroscopy. Finally, 2,4-dichlorphenoxyacetic acid (2,4-D) was used as probe, the photocatalytic properties of RGO/nanoTiO2 composites in anoxic water and the degradation mechanics of 2,4-D were studied. The results show that less reactive groups are generated on six carbon ring of GO when adopting the Hummers method of low temperature oxidation, the rings structure can be well repaired by using ultrasonic/ultraviolet light reduction process and the coupled high temperature thermal reduction process. The prepared RGO/nanoTiO2 composites have good performances of 2,4-D degradation, under the anoxic condition, 2,4-D mainly conducts photocatalytic reduction reaction, the chlorines on benzene ring are removed and produces middle products such as chlorophenol, pyrogallol, phloroglucinol and so on, part of the 2,4-D is oxydative degraded to generate CO2 and H2O. The obtained conclusions indicate that the prepared RGO/nanoTiO2 composites have good photocatalytic reduction performances.
In order to explore the method of using ultraviolet light and coupled thermal reduction process to prepare RGO/nanoTiO2 composites under the assistance of ultrasonic and investigate the photocatalytic reduction performance in the anoxic water, graphene oxide (GO) was prepared by improved Hummers method using flake graphite as raw material, and reduced graphene oxide (RGO) was prepared by ultrasonic/ultraviolet light reduction process firstly. Then, butyl titanate ester and RGO were used as precursors, RGO/nanoTiO2 composite photocatalytic materials were prepared by the method of sol-gel and high temperature heating under nitrogen protection. After that, the structure and properties of RGO/nanoTiO2 composites were characterized by FTIR, XRD, BET and ultraviolet-visible spectroscopy. Finally, 2,4-dichlorphenoxyacetic acid (2,4-D) was used as probe, the photocatalytic properties of RGO/nanoTiO2 composites in anoxic water and the degradation mechanics of 2,4-D were studied. The results show that less reactive groups are generated on six carbon ring of GO when adopting the Hummers method of low temperature oxidation, the rings structure can be well repaired by using ultrasonic/ultraviolet light reduction process and the coupled high temperature thermal reduction process. The prepared RGO/nanoTiO2 composites have good performances of 2,4-D degradation, under the anoxic condition, 2,4-D mainly conducts photocatalytic reduction reaction, the chlorines on benzene ring are removed and produces middle products such as chlorophenol, pyrogallol, phloroglucinol and so on, part of the 2,4-D is oxydative degraded to generate CO2 and H2O. The obtained conclusions indicate that the prepared RGO/nanoTiO2 composites have good photocatalytic reduction performances.
2016, 33(1): 163-173.
doi: 10.13801/j.cnki.fhclxb.20150410.003
Abstract:
The time-dependent behavior and the affecting factors of preload relaxation in carbon/epoxy composite bolted joint have been studied, through a forced bending vibration test included various initial preloads and excitation frequencies. Analysis method and test method, based on modal parameters (resonance frequency and damping ratio), were utilized to characterize the dynamic property of bolted joints. It is observed that the loss degree of preload will increase with decreasing initial preload, and it will increase with the exciting frequency increasing, over a period of 10 h vibration fatigue process. Vibration fatigue damages would result in stiffness decay and damping increase in structural joints; the relaxation in composite bolted joints can be attributed to the conjunct mechanisms between viscoelastic behavior of materials and interface friction of which about 50% of relaxation is due to viscoelastic effect of composites.
The time-dependent behavior and the affecting factors of preload relaxation in carbon/epoxy composite bolted joint have been studied, through a forced bending vibration test included various initial preloads and excitation frequencies. Analysis method and test method, based on modal parameters (resonance frequency and damping ratio), were utilized to characterize the dynamic property of bolted joints. It is observed that the loss degree of preload will increase with decreasing initial preload, and it will increase with the exciting frequency increasing, over a period of 10 h vibration fatigue process. Vibration fatigue damages would result in stiffness decay and damping increase in structural joints; the relaxation in composite bolted joints can be attributed to the conjunct mechanisms between viscoelastic behavior of materials and interface friction of which about 50% of relaxation is due to viscoelastic effect of composites.
2016, 33(1): 174-182.
doi: 10.13801/j.cnki.fhclxb.20150429.001
Abstract:
Aimed at the meso-structure of crossover and undulation region in filament wound composites, a meso-scale analytical model is proposed. First, the crossover and undulation region are classified to two types, i.e. the circumferential crossover and undulation region, and the helical crossover and undulation region. Next, based on the filament wound surface, parallel cross-section was used to discrete spatial structure model of undulation region, which will be discretized to numbers of sub-models to describe the meso-structure of crossover and undulation region of filament wound composites by using meso-parameters such as fiber bundle inclination angle, size of resin rich area, volume fraction, cross-section shape and size of fiber bundle. With this meso-scale model and the laminate theory, a method for calculating the equivalent stiffness of crossover and undulation region of filament wound composites is eventually established. The effects of cross-section, inclination angle of fiber bundle and the volume fraction of resin rich area on local area equivalent stiffness were studied. The results show that the elastic modulus for circumferential crossover and undulation region decreases to greater extent as compared that of the helical crossover and undulation region. Significant decrease in elastic modulus and shear modulus and increase in Poisson's ratio are found for resin rich area. Thickness increase and cross-section change of fiber bundle have evident effects on the equivalent stiffness of crossover and undulation region.
Aimed at the meso-structure of crossover and undulation region in filament wound composites, a meso-scale analytical model is proposed. First, the crossover and undulation region are classified to two types, i.e. the circumferential crossover and undulation region, and the helical crossover and undulation region. Next, based on the filament wound surface, parallel cross-section was used to discrete spatial structure model of undulation region, which will be discretized to numbers of sub-models to describe the meso-structure of crossover and undulation region of filament wound composites by using meso-parameters such as fiber bundle inclination angle, size of resin rich area, volume fraction, cross-section shape and size of fiber bundle. With this meso-scale model and the laminate theory, a method for calculating the equivalent stiffness of crossover and undulation region of filament wound composites is eventually established. The effects of cross-section, inclination angle of fiber bundle and the volume fraction of resin rich area on local area equivalent stiffness were studied. The results show that the elastic modulus for circumferential crossover and undulation region decreases to greater extent as compared that of the helical crossover and undulation region. Significant decrease in elastic modulus and shear modulus and increase in Poisson's ratio are found for resin rich area. Thickness increase and cross-section change of fiber bundle have evident effects on the equivalent stiffness of crossover and undulation region.
2016, 33(1): 183-188.
doi: 10.13801/j.cnki.fhclxb.20150514.001
Abstract:
Based on the proposed basic mechanical hypothesis and calculation analytical model of unidirectional stiffener composite panel unit, a method was developed for analyzing structure efficiency quickly under the multi-constraint case. Analysis and optimization of structure efficiency for typical unidirectional stiffener composite panel was done using present method. And the structure efficiency variation trend which changes with the design parameters was obtained as well as the relatively optimum structure parameters. Present method synthetically accounts for the global stability of stiffener, local stability, static strength constrains of structure and interaction of them. Upon the basic hypothesis, the discrete variables of composite structure change to independent continuous design variables, thus it can observably simplify the analysis of structure mechanical properties and optimization. Results from the test and finite element analysis were compared with those from the present method, and they exhibit in good agreements. The research results can directly provide reference for the design of the unidirectional stiffener composite panels. And the method has good practical engineering application and reference value.
Based on the proposed basic mechanical hypothesis and calculation analytical model of unidirectional stiffener composite panel unit, a method was developed for analyzing structure efficiency quickly under the multi-constraint case. Analysis and optimization of structure efficiency for typical unidirectional stiffener composite panel was done using present method. And the structure efficiency variation trend which changes with the design parameters was obtained as well as the relatively optimum structure parameters. Present method synthetically accounts for the global stability of stiffener, local stability, static strength constrains of structure and interaction of them. Upon the basic hypothesis, the discrete variables of composite structure change to independent continuous design variables, thus it can observably simplify the analysis of structure mechanical properties and optimization. Results from the test and finite element analysis were compared with those from the present method, and they exhibit in good agreements. The research results can directly provide reference for the design of the unidirectional stiffener composite panels. And the method has good practical engineering application and reference value.
2016, 33(1): 189-197.
doi: 10.13801/j.cnki.fhclxb.20150417.001
Abstract:
The mechanical behavior of imperfect particle/matrix interface in particle-reinforced composites (PRCs) are defined by the cohesive zone model (CZM). Using mesoscopic mechanical Mori-Tanaka (M-T) method and dilute solution method, we studied the effect of imperfect interface stiffness on the effective modulus of composites. Results present that the monotonic increasing relation curves exist between the effective modulus and the particle/matrix imperfect interface stiffness for the composite with a certain volume fraction.The relation curves between the effective modulus and the imperfect interface stiffness with different volume fractions accounting for a certain composites converge to a unique critical point (CP), and the critical interfacial stiffness characterized by CP dominates the way of how volume fraction of particle affects the effective modulus. The effects of mechanical property of matrix and reinforcement phase, reinforced particle size on the critical interfacial stiffness of CP were studied. With effective modulus-interfacial stiffness relation curves and the experimental effective modulus, the estimated method of the imperfect interfacial stiffness for PRCs was proposed. The macro effective modulus of the composites was then predicted.
The mechanical behavior of imperfect particle/matrix interface in particle-reinforced composites (PRCs) are defined by the cohesive zone model (CZM). Using mesoscopic mechanical Mori-Tanaka (M-T) method and dilute solution method, we studied the effect of imperfect interface stiffness on the effective modulus of composites. Results present that the monotonic increasing relation curves exist between the effective modulus and the particle/matrix imperfect interface stiffness for the composite with a certain volume fraction.The relation curves between the effective modulus and the imperfect interface stiffness with different volume fractions accounting for a certain composites converge to a unique critical point (CP), and the critical interfacial stiffness characterized by CP dominates the way of how volume fraction of particle affects the effective modulus. The effects of mechanical property of matrix and reinforcement phase, reinforced particle size on the critical interfacial stiffness of CP were studied. With effective modulus-interfacial stiffness relation curves and the experimental effective modulus, the estimated method of the imperfect interfacial stiffness for PRCs was proposed. The macro effective modulus of the composites was then predicted.
2016, 33(1): 198-203.
doi: 10.13801/j.cnki.fhclxb.20150528.005
Abstract:
The response behaviors of the interior of carbon fiber composites under the effects of electric-thermal load were very complicated for the composites had the characteristics of composition complexity, anisotropy and so on. In order to investigate the electric-thermal response of carbon fiber composites, self-devised electric-thermal damage test device was adopted, the temperature distribution on the surface of carbon fiber multifilament specimens under different current intensities was tested and the changing rules of the resistance of carbon fiber multifilament versus temperature were obtained firstly, and carbon fiber multifilament which had temperature-sensitive effect was preliminarily revealed. Then, the changing rules of tensile strength, elongation at break and tensile modulus under different current treatment conditions were investigated, and the morphology and microstructure changing of the materials before and after current treatment were analyzed by SEM and FTIR. The investigation results indicate that the heating effects of fibers in the galvanization promote the further solidification of the matrix, and improve the interfacial adhesion property of multifilament at the same time. However, when the current intensity is too high, the tensile strength of multifilament will decrease for the damage of fibers themselves or ablative degradation on matrix and interface layer, thus reduce the properties of carbon fiber composites.
The response behaviors of the interior of carbon fiber composites under the effects of electric-thermal load were very complicated for the composites had the characteristics of composition complexity, anisotropy and so on. In order to investigate the electric-thermal response of carbon fiber composites, self-devised electric-thermal damage test device was adopted, the temperature distribution on the surface of carbon fiber multifilament specimens under different current intensities was tested and the changing rules of the resistance of carbon fiber multifilament versus temperature were obtained firstly, and carbon fiber multifilament which had temperature-sensitive effect was preliminarily revealed. Then, the changing rules of tensile strength, elongation at break and tensile modulus under different current treatment conditions were investigated, and the morphology and microstructure changing of the materials before and after current treatment were analyzed by SEM and FTIR. The investigation results indicate that the heating effects of fibers in the galvanization promote the further solidification of the matrix, and improve the interfacial adhesion property of multifilament at the same time. However, when the current intensity is too high, the tensile strength of multifilament will decrease for the damage of fibers themselves or ablative degradation on matrix and interface layer, thus reduce the properties of carbon fiber composites.
2016, 33(1): 204-212.
doi: 10.13801/j.cnki.fhclxb.20150518.005
Abstract:
In order to predict the low-velocity impact characteristics of composite laminates, a simulation method for impacting delamination response was proposed based on spring-mass model. First, the changes of flexural rigidity and deflection before and after delamination were calculated according to the presupposed delamination number and delamination area, therefore the time histories of tup motions with the delamination event was simulated. Then, contact force was calculated by the acceleration of tup, and the permanent indentation depth was calculated based on the elasto-plastic contact law of material. Whereafter, the low-velocity impact experiment was carried out on the panel of co-curing composite wing box, and the impact sites were divided into three types: the mid-point position of the skin between two spars, the boundary of the T joint bonding area of skin and spar, and the point just over the spar. After that, the characterstics of contact force, delamination threshold force and indentation depth of different impact sites were contrasted and analyzed. Finally, the contact force, permanent indentation depth and absorbed energy of impact site of the 1st type were calculated by the proposed model, as well as the influences of length-width ratio of rectangle plate on the membrane stiffness and contact force were also analyzed. The results show that the simulated contact force is well agreed with the measured result, and the accuracy of simulations for permanent indentation depth and absorbed energy are also acceptable, thus the proposed model is available. The membrane stiffness increases rapidly with the length-width ratio decreasing, thereby promotes the contact force increase significantly.
In order to predict the low-velocity impact characteristics of composite laminates, a simulation method for impacting delamination response was proposed based on spring-mass model. First, the changes of flexural rigidity and deflection before and after delamination were calculated according to the presupposed delamination number and delamination area, therefore the time histories of tup motions with the delamination event was simulated. Then, contact force was calculated by the acceleration of tup, and the permanent indentation depth was calculated based on the elasto-plastic contact law of material. Whereafter, the low-velocity impact experiment was carried out on the panel of co-curing composite wing box, and the impact sites were divided into three types: the mid-point position of the skin between two spars, the boundary of the T joint bonding area of skin and spar, and the point just over the spar. After that, the characterstics of contact force, delamination threshold force and indentation depth of different impact sites were contrasted and analyzed. Finally, the contact force, permanent indentation depth and absorbed energy of impact site of the 1st type were calculated by the proposed model, as well as the influences of length-width ratio of rectangle plate on the membrane stiffness and contact force were also analyzed. The results show that the simulated contact force is well agreed with the measured result, and the accuracy of simulations for permanent indentation depth and absorbed energy are also acceptable, thus the proposed model is available. The membrane stiffness increases rapidly with the length-width ratio decreasing, thereby promotes the contact force increase significantly.
2016, 33(1): 213-223.
doi: 10.13801/j.cnki.fhclxb.20150424.002
Abstract:
In order to investigate the tensile mechanical properties of Kevlar 49 single filament (microcosmic) and single yarn (mesoscopic), MTI miniature tensile tester and MTS microcomputer control electron universal testing machine were used respectively to conduct the unidirectional tensile tests on filament and yarn firstly, and found that there was a significant correlation between the mechanical properties of filament and yarn as well as gauge length and structural length scale of samples. The tensile strength of samples decreased with the increasing gauge length and structural length scale enlarged from filament to yarn. Then, the testing data was statistically analyzed according to Weibull distribution, and the random variability degree for tensile strength of filaments and yarns under different gauge lengths was quantified. After that, for the tensile strength of filament according with the Weibull distribution and probabilistic failure, user-defined subroutine (USERMAT) in ANSYS was used to establish the filament constitutive model. Finally, the filament constitutive model was used to simulate the tensile failure behaviors of yarn, and the effects of key parameters on tensile failure behaviors of yarns were also discussed. The results show that the goodness of fit between simulated results and testing results of yarn is preferable, and the established USERMAT can predict the tensile properties of yarn comparatively accurately.
In order to investigate the tensile mechanical properties of Kevlar 49 single filament (microcosmic) and single yarn (mesoscopic), MTI miniature tensile tester and MTS microcomputer control electron universal testing machine were used respectively to conduct the unidirectional tensile tests on filament and yarn firstly, and found that there was a significant correlation between the mechanical properties of filament and yarn as well as gauge length and structural length scale of samples. The tensile strength of samples decreased with the increasing gauge length and structural length scale enlarged from filament to yarn. Then, the testing data was statistically analyzed according to Weibull distribution, and the random variability degree for tensile strength of filaments and yarns under different gauge lengths was quantified. After that, for the tensile strength of filament according with the Weibull distribution and probabilistic failure, user-defined subroutine (USERMAT) in ANSYS was used to establish the filament constitutive model. Finally, the filament constitutive model was used to simulate the tensile failure behaviors of yarn, and the effects of key parameters on tensile failure behaviors of yarns were also discussed. The results show that the goodness of fit between simulated results and testing results of yarn is preferable, and the established USERMAT can predict the tensile properties of yarn comparatively accurately.
