2016 Vol. 33, No. 3
2016, 33(3): 431-450.
doi: 10.13801/j.cnki.fhclxb.20160219.001
Abstract:
Fluorescent carbon dots are one of the most popular carbon nanomaterials after carbon nanotube, nano-diamond and graphene. Owing to its advantages of excellent photoluminescence, small size features, good biocompatibility, low cytotoxicity and ease to achieve surface functionalization compared with conventional semiconductor quantum dots, carbon dots have great application value in the field of environmental detection, biochemical sensing, drug carriers, photocatalytic and electrocatalytic technology and other areas. The progress in composition methods, structure, property and application research of carbon dots are summarized, the bottleneck problems of restricting carbon dots application development are pointed out and main further research direction is prospected.
Fluorescent carbon dots are one of the most popular carbon nanomaterials after carbon nanotube, nano-diamond and graphene. Owing to its advantages of excellent photoluminescence, small size features, good biocompatibility, low cytotoxicity and ease to achieve surface functionalization compared with conventional semiconductor quantum dots, carbon dots have great application value in the field of environmental detection, biochemical sensing, drug carriers, photocatalytic and electrocatalytic technology and other areas. The progress in composition methods, structure, property and application research of carbon dots are summarized, the bottleneck problems of restricting carbon dots application development are pointed out and main further research direction is prospected.
2016, 33(3): 451-458.
doi: 10.13801/j.cnki.fhclxb.20150611.003
Abstract:
In order to investigate the effects of epoxidation on the dispersibility of silica (SiO2 particles) in solution-polymerized styrene butadiene rubber (SSBR) matrix, SSBR and epoxidized solution-polymerized styrene butadiene rubber (ESSBR) were used as matrix, silica were used as reinforcer firstly, SiO2/SSBR and SiO2/ESSBR rubber compounds and vulcanizates were prepared, respectively. Then, the structure, morphology, vulcanization characteristics, wear resistance, quasi-static mechanical properties and dynamic mechanical properties of the materials were investigated by FTIR, SEM and other testing methods. The results show that the Mooney viscosity of crude rubbers increases with the epoxidation degree growing from 0 to 14.73%. The epoxy groups in ESSBR chains react with the silanol groups on the surfaces of SiO2 particles, thus forms stable chemical bonds which depress the aggregation of SiO2 particles and promotes the uniform desperation of them. When the epoxidation degree is 6.87%, SiO2 particles have the best dispersity in ESSBR. With the epoxidation degree increasing, the tensile strength of SiO2/ESSBR vulcanizates increases firstly and then decreases, wear resistance enhances firstly and then reduces, the elongation at break decreases, stretching strengths at 100% and 300% increase, glass transition temperature increases, loss factor at 0℃ increases significantly, wet-skid resistance enhances, loss factor at 60℃ increases slightly and rolling resistance increases. Therefore, the comprehensive performances of SSBR vulcanizates after epoxidation modification enhance, when the epoxidation degree is within the scope of 6.87%-8.51%, the comprehensive performance of SiO2/ESSBR vulcanizate reaches the best.
In order to investigate the effects of epoxidation on the dispersibility of silica (SiO2 particles) in solution-polymerized styrene butadiene rubber (SSBR) matrix, SSBR and epoxidized solution-polymerized styrene butadiene rubber (ESSBR) were used as matrix, silica were used as reinforcer firstly, SiO2/SSBR and SiO2/ESSBR rubber compounds and vulcanizates were prepared, respectively. Then, the structure, morphology, vulcanization characteristics, wear resistance, quasi-static mechanical properties and dynamic mechanical properties of the materials were investigated by FTIR, SEM and other testing methods. The results show that the Mooney viscosity of crude rubbers increases with the epoxidation degree growing from 0 to 14.73%. The epoxy groups in ESSBR chains react with the silanol groups on the surfaces of SiO2 particles, thus forms stable chemical bonds which depress the aggregation of SiO2 particles and promotes the uniform desperation of them. When the epoxidation degree is 6.87%, SiO2 particles have the best dispersity in ESSBR. With the epoxidation degree increasing, the tensile strength of SiO2/ESSBR vulcanizates increases firstly and then decreases, wear resistance enhances firstly and then reduces, the elongation at break decreases, stretching strengths at 100% and 300% increase, glass transition temperature increases, loss factor at 0℃ increases significantly, wet-skid resistance enhances, loss factor at 60℃ increases slightly and rolling resistance increases. Therefore, the comprehensive performances of SSBR vulcanizates after epoxidation modification enhance, when the epoxidation degree is within the scope of 6.87%-8.51%, the comprehensive performance of SiO2/ESSBR vulcanizate reaches the best.
2016, 33(3): 459-468.
doi: 10.13801/j.cnki.fhclxb.20150706.003
Abstract:
In order to investigate the mechanical response and failure behavior of Kevlar 49 aramid fabric reinforced epoxy polymers under the coupling effect of medium strain rates and different temperatures, MTS high rate servo-hydraulic testing machine was utilized to conduct the unidirectional dynamic tensile tests of aramid fiber reinforced polymers (AFRP) under different initial strain rates (25, 50, 100, 200 s-1) and temperatures (-25, 0, 25, 50, 100℃) firstly. Then, Weibull analysis model was used to quantify the variability degree of tensile strength under different strain rates and temperatures. The results show that under the same temperature (25℃), with the increasing strain rate, elastic modulus and tensile strength both increase firstly (when initial strain rate is in the range of 25-50 s-1) and then decrease (when initial strain rate is in the range of 50-200 s-1), while the ultimate strain presents an opposite changing trend, and the changing extent of toughness with strain rate is not obvious. Under the same initial strain rate (25 s-1) and comparing with the situation under 25℃, the temperature increasing or decreasing will leads to the decrease of elastic modulus, and the ultimate strain increases significantly when the temperature is 100℃, while tensile strength and toughness both change little with the variation of temperature. The comparison and analysis for failure morphologies of AFRP show that the failure patterns of AFRP under different test conditions are almost the same, which present relatively smooth failure surfaces. The conclusions obtained can provide references for the theoretical investigation and application of AFRP under the effects of extreme loading and environment.
In order to investigate the mechanical response and failure behavior of Kevlar 49 aramid fabric reinforced epoxy polymers under the coupling effect of medium strain rates and different temperatures, MTS high rate servo-hydraulic testing machine was utilized to conduct the unidirectional dynamic tensile tests of aramid fiber reinforced polymers (AFRP) under different initial strain rates (25, 50, 100, 200 s-1) and temperatures (-25, 0, 25, 50, 100℃) firstly. Then, Weibull analysis model was used to quantify the variability degree of tensile strength under different strain rates and temperatures. The results show that under the same temperature (25℃), with the increasing strain rate, elastic modulus and tensile strength both increase firstly (when initial strain rate is in the range of 25-50 s-1) and then decrease (when initial strain rate is in the range of 50-200 s-1), while the ultimate strain presents an opposite changing trend, and the changing extent of toughness with strain rate is not obvious. Under the same initial strain rate (25 s-1) and comparing with the situation under 25℃, the temperature increasing or decreasing will leads to the decrease of elastic modulus, and the ultimate strain increases significantly when the temperature is 100℃, while tensile strength and toughness both change little with the variation of temperature. The comparison and analysis for failure morphologies of AFRP show that the failure patterns of AFRP under different test conditions are almost the same, which present relatively smooth failure surfaces. The conclusions obtained can provide references for the theoretical investigation and application of AFRP under the effects of extreme loading and environment.
2016, 33(3): 469-476.
doi: 10.13801/j.cnki.fhclxb.20150615.001
Abstract:
In order to investigate the influences of foaming agent azodicarbonamide (AC) additive amount on the thermo-stability, microstructure and chemical structure of wheat straw/polypropylene (PP) foamed composites, TG-DSC, FTIR and stereomicroscope were used to analyze the thermo-stability, chemical structure and microstructure of wheat straw/PP foamed composites, and linear expansion coefficient, thermal conductivity, apparent density and mechanical properties of composites were also measured. The results show that AC additive amount and its thermal decomposition degree both have great influences on the thermo-stability, pore structure and thermal expansion properties of wheat straw/PP foamed composites. When AC additive amount is 1.0wt%, the thermal decomposition degree is the highest, and the composites have relatively preferable thermo-stability, the pore structure is homogeneous, interface between wheat straw and matrix is stable, and the linear expansion coefficient is the lowest. The conclusions obtained indicate that when AC additive amount is 1.0wt%, the wheat straw/PP foamed composites have relatively preferable comprehensive performance.
In order to investigate the influences of foaming agent azodicarbonamide (AC) additive amount on the thermo-stability, microstructure and chemical structure of wheat straw/polypropylene (PP) foamed composites, TG-DSC, FTIR and stereomicroscope were used to analyze the thermo-stability, chemical structure and microstructure of wheat straw/PP foamed composites, and linear expansion coefficient, thermal conductivity, apparent density and mechanical properties of composites were also measured. The results show that AC additive amount and its thermal decomposition degree both have great influences on the thermo-stability, pore structure and thermal expansion properties of wheat straw/PP foamed composites. When AC additive amount is 1.0wt%, the thermal decomposition degree is the highest, and the composites have relatively preferable thermo-stability, the pore structure is homogeneous, interface between wheat straw and matrix is stable, and the linear expansion coefficient is the lowest. The conclusions obtained indicate that when AC additive amount is 1.0wt%, the wheat straw/PP foamed composites have relatively preferable comprehensive performance.
2016, 33(3): 477-485.
doi: 10.13801/j.cnki.fhclxb.20150623.004
Abstract:
In order to enhance the comprehensive properties of wood plastic composites by using glass fiber and investigate the effect laws of glass fiber content on the properties of bamboo flour/high density polyethylene (HDPE) composites, the surfaces of bamboo flour were modified by A-171 silane coupling agent and a certain amount of glass fiber were added firstly. Then, glass fiber-bamboo flour/HDPE composites were prepared by hot pressing molding technology. Finally, the influences of glass fiber content on the mechanical properties, thermal properties and tribological behaviors of the composites were observed, and the morphologies of fracture surfaces and worn surfaces of the materials were observed by SEM. The results show that when the glass fiber content is 3wt%, the tensile strength and flexural strength of bamboo flour/HDPE composites can be enhanced significantly; comparing with the composite without the addition of glass fiber, the tensile strength and flexural strength of composites after the addition of glass fiber increase by 19.41% and 23.54% respectively. The coefficient of linear expansion of composites in length-width direction decreases obviously with the glass fiber content increasing during the temperature range of 30-60℃, while the coefficient of linear expansion of the same composite gradually increases with the temperature increasing. In nitrogen atmosphere, with the glass fiber content increasing, the friction coefficient of bamboo flour/HDPE composites increases gradually at first and then almost remains unchanged, and the wear rate decreases gradually. The conclusions obtained show that the wood plastic composite products with the glass fiber content of 3wt%-7wt% are suitable for construction beams (such as pavilions or bridges et al), while the wood plastic composite products with the glass fiber content of 7wt%-10wt% are suitable for the ground pavement for places with large flow of people (such as park or recreational greenway et al).
In order to enhance the comprehensive properties of wood plastic composites by using glass fiber and investigate the effect laws of glass fiber content on the properties of bamboo flour/high density polyethylene (HDPE) composites, the surfaces of bamboo flour were modified by A-171 silane coupling agent and a certain amount of glass fiber were added firstly. Then, glass fiber-bamboo flour/HDPE composites were prepared by hot pressing molding technology. Finally, the influences of glass fiber content on the mechanical properties, thermal properties and tribological behaviors of the composites were observed, and the morphologies of fracture surfaces and worn surfaces of the materials were observed by SEM. The results show that when the glass fiber content is 3wt%, the tensile strength and flexural strength of bamboo flour/HDPE composites can be enhanced significantly; comparing with the composite without the addition of glass fiber, the tensile strength and flexural strength of composites after the addition of glass fiber increase by 19.41% and 23.54% respectively. The coefficient of linear expansion of composites in length-width direction decreases obviously with the glass fiber content increasing during the temperature range of 30-60℃, while the coefficient of linear expansion of the same composite gradually increases with the temperature increasing. In nitrogen atmosphere, with the glass fiber content increasing, the friction coefficient of bamboo flour/HDPE composites increases gradually at first and then almost remains unchanged, and the wear rate decreases gradually. The conclusions obtained show that the wood plastic composite products with the glass fiber content of 3wt%-7wt% are suitable for construction beams (such as pavilions or bridges et al), while the wood plastic composite products with the glass fiber content of 7wt%-10wt% are suitable for the ground pavement for places with large flow of people (such as park or recreational greenway et al).
2016, 33(3): 486-494.
doi: 10.13801/j.cnki.fhclxb.20160309.004
Abstract:
In order to improve the barrier and antistatic properties of thermoplastic polyurethane (TPU), original carbon nanotubes (CNTs) were added into functional modification reduced graphene oxide (FRGO), and hybrid particles FRGO-CNTs which were uniformly dispersed in N, N-dimethylformamide (DMF) were prepared by non-covalent modification firstly. Then, FRGO-CNTs/TPU composite films were fabricated by solution coating method on the coating machine. Finally, the structures and properties of FRGO-CNTs/TPU composite films were characterized by FTIR, XRD, XPS, FE-SEM, TG, oxygen transmission rate tester, high resistance meter and universal testing machine. The results demonstrate that FRGO and CNTs produce synergistic effect through π-π conjugation, and the prepared FRGO-CNTs show good compatibility with TPU matrix. When FRGO-CNTs content (using TPU as reference) is 2.0wt%, the thermal decomposition temperature of composite film increases by 49℃, and the oxygen transmission rate decreases by 53.7%. The FRGO with large specific surface area and the CNTs with high length to diameter ratio can build the conductive network in TPU matrix. When FRGO-CNTs content is only 0.8wt%, the volume resistivity of FRGO-CNTs/TPU composite film declines by as much as 7 orders of magnitude. Meanwhile, with the FRGO-CNTs content increasing, the tensile strength and elongation at break of composite films both rise at first and then go down.
In order to improve the barrier and antistatic properties of thermoplastic polyurethane (TPU), original carbon nanotubes (CNTs) were added into functional modification reduced graphene oxide (FRGO), and hybrid particles FRGO-CNTs which were uniformly dispersed in N, N-dimethylformamide (DMF) were prepared by non-covalent modification firstly. Then, FRGO-CNTs/TPU composite films were fabricated by solution coating method on the coating machine. Finally, the structures and properties of FRGO-CNTs/TPU composite films were characterized by FTIR, XRD, XPS, FE-SEM, TG, oxygen transmission rate tester, high resistance meter and universal testing machine. The results demonstrate that FRGO and CNTs produce synergistic effect through π-π conjugation, and the prepared FRGO-CNTs show good compatibility with TPU matrix. When FRGO-CNTs content (using TPU as reference) is 2.0wt%, the thermal decomposition temperature of composite film increases by 49℃, and the oxygen transmission rate decreases by 53.7%. The FRGO with large specific surface area and the CNTs with high length to diameter ratio can build the conductive network in TPU matrix. When FRGO-CNTs content is only 0.8wt%, the volume resistivity of FRGO-CNTs/TPU composite film declines by as much as 7 orders of magnitude. Meanwhile, with the FRGO-CNTs content increasing, the tensile strength and elongation at break of composite films both rise at first and then go down.
2016, 33(3): 495-502.
doi: 10.13801/j.cnki.fhclxb.20150727.001
Abstract:
In order to broaden the engineering application areas of polyamide 6 (PA6), LiCl/PA6 composites were prepared by melting extrusion firstly. Then, the effects of LiCl content on crystallization behaviors and mechanical properties of PA6 as well as the restricted mechanisms of crystallization were investigated by XRD, DSC, rheometer and electronic tensile testing machine et al. The results show that with LiCl content increasing, the temperature of nucleation, the growth temperature and melt temperature of spherulites of LiCl/PA6 composite systems all move toward low temperature direction; the density and rate of nucleation both decrease gradually, which leads to the decrease of crystallization ability, and the crystallinity decreases from the original 36.5% to 5.6%; the crystallinity of γ-crystal decreases gradually, while the crystallinity of α-crystal initially increases and then decreases, transformation occurs between γ-crystal and α-crystal. In addition, the tensile strength and impact strength of LiCl/PA6 composites both increase firstly and then decrease, when LiCl content is 6.0wt%, impact strength reaches the maximum 7.9 kJ/m2, which is 1.44 times of the impact strength of pure PA6 (5.5 kJ/m2).
In order to broaden the engineering application areas of polyamide 6 (PA6), LiCl/PA6 composites were prepared by melting extrusion firstly. Then, the effects of LiCl content on crystallization behaviors and mechanical properties of PA6 as well as the restricted mechanisms of crystallization were investigated by XRD, DSC, rheometer and electronic tensile testing machine et al. The results show that with LiCl content increasing, the temperature of nucleation, the growth temperature and melt temperature of spherulites of LiCl/PA6 composite systems all move toward low temperature direction; the density and rate of nucleation both decrease gradually, which leads to the decrease of crystallization ability, and the crystallinity decreases from the original 36.5% to 5.6%; the crystallinity of γ-crystal decreases gradually, while the crystallinity of α-crystal initially increases and then decreases, transformation occurs between γ-crystal and α-crystal. In addition, the tensile strength and impact strength of LiCl/PA6 composites both increase firstly and then decrease, when LiCl content is 6.0wt%, impact strength reaches the maximum 7.9 kJ/m2, which is 1.44 times of the impact strength of pure PA6 (5.5 kJ/m2).
2016, 33(3): 503-509.
doi: 10.13801/j.cnki.fhclxb.20150528.006
Abstract:
Polymer high-voltage direct current cables accompany with the injection of electrons and holes of insulating layer which accumulated in local polymer will form space charge packet and trigger insulation breakdown in electric power transmission. Therefore, the key technology of preparing polymer high-voltage direct current cables is to suppress the injection and accumulation of electrons and holes, prevent the formation of space charge packet. By preparing the multi-layer mesoporous structure nano MgO, uniform dispersion of nano MgO in low density polyethylene (LDPE) was realized by using the low boiling point solvent method. The characteristics of space charge, direct current breakdown strength, thermally stimulated current and dielectric properties of 1wt% nano MgO/LDPE composites were studied. The results reveal that adding 1wt% nano MgO into LDPE can effectively suppress space charge accumulation under the 70 kV/mm electric field, improving direct current breakdown strength, decreasing the dielectric permittivity. Thermally stimulated current research shows that nano MgO induces new traps, effectively captures charge carriers and independent electrical field forms, avoids local effective electrical field, forms a new barrier, suppresses the injection of electrode carrier, and suppresses space charge accumulation eventually.
Polymer high-voltage direct current cables accompany with the injection of electrons and holes of insulating layer which accumulated in local polymer will form space charge packet and trigger insulation breakdown in electric power transmission. Therefore, the key technology of preparing polymer high-voltage direct current cables is to suppress the injection and accumulation of electrons and holes, prevent the formation of space charge packet. By preparing the multi-layer mesoporous structure nano MgO, uniform dispersion of nano MgO in low density polyethylene (LDPE) was realized by using the low boiling point solvent method. The characteristics of space charge, direct current breakdown strength, thermally stimulated current and dielectric properties of 1wt% nano MgO/LDPE composites were studied. The results reveal that adding 1wt% nano MgO into LDPE can effectively suppress space charge accumulation under the 70 kV/mm electric field, improving direct current breakdown strength, decreasing the dielectric permittivity. Thermally stimulated current research shows that nano MgO induces new traps, effectively captures charge carriers and independent electrical field forms, avoids local effective electrical field, forms a new barrier, suppresses the injection of electrode carrier, and suppresses space charge accumulation eventually.
2016, 33(3): 510-515.
doi: 10.13801/j.cnki.fhclxb.20150616.001
Abstract:
The influences of curing reaction temperature and time, toughening agent and thickening agent addition amounts on rheological properties of phenolic resin were investigated using rheometer. The glass fiber reinforced phenolic prepregs were also prepared to fabricate glass fiber/phenolic-Nomex honeycomb cored sandwich composites by co-curing technology with Nomex honeycomb core, and the adhesion properties of skin-core were measured. The results show that the viscosity of the modified phenolic resin at elevated temperature increases a lot and flow behavior is also well improved, the interfacial adhesion between the as-prepared prepreg and Nomex honeycomb core enhances obviously and the climb drum peel strength of the as-prepared sandwich panel can achieve to above 15 N·mm/mm when the mass ratios of toughening agent and thickening agent addition amounts are 5% and 3% to the pure phenolic resin, indicating the self-adhesive characteristics of the modified phenolic resin and its prepreg. Additionally, it can further increase the adhesion strength of skin-core for glass fiber/phenolic-Nomex honeycomb cored sandwich composite by applying a moderate heating profile in co-curing process.
The influences of curing reaction temperature and time, toughening agent and thickening agent addition amounts on rheological properties of phenolic resin were investigated using rheometer. The glass fiber reinforced phenolic prepregs were also prepared to fabricate glass fiber/phenolic-Nomex honeycomb cored sandwich composites by co-curing technology with Nomex honeycomb core, and the adhesion properties of skin-core were measured. The results show that the viscosity of the modified phenolic resin at elevated temperature increases a lot and flow behavior is also well improved, the interfacial adhesion between the as-prepared prepreg and Nomex honeycomb core enhances obviously and the climb drum peel strength of the as-prepared sandwich panel can achieve to above 15 N·mm/mm when the mass ratios of toughening agent and thickening agent addition amounts are 5% and 3% to the pure phenolic resin, indicating the self-adhesive characteristics of the modified phenolic resin and its prepreg. Additionally, it can further increase the adhesion strength of skin-core for glass fiber/phenolic-Nomex honeycomb cored sandwich composite by applying a moderate heating profile in co-curing process.
2016, 33(3): 516-524.
doi: 10.13801/j.cnki.fhclxb.20150612.001
Abstract:
In machining of carbon fiber reinforced polymer (CFRP), the matrix phase is easy to fail due to the excessive cutting force, which extends to the underneath of machining surface and forms damage rapidly. For the precise prediction and control of cutting force, we established an artificial neural network cutting force model based on the experimental cutting force data to predict the cutting force change rule in machining CFRP under different fiber orientations, cutting depths and tool angles. Orthogonal cutting experiments on CFRP unidirectional laminate of typical fiber orientation with different tool angles and cutting parameters were conducted to verify the predicting model, and the predicting precision is up to 85%. Combined with the online microscopic prediction results of chip forming process, it is concluded that the fiber orientation is the primary factor affecting the cutting forces of CFRP, as varies from 0° to 135°, chip formation ways include the crushing-dominated failure type and bending failure type; the cutting force firstly decreases and then increases as the fiber orientation angle increases, and is maximum at 135°; the cutting force increases generally as cutting depth increases.
In machining of carbon fiber reinforced polymer (CFRP), the matrix phase is easy to fail due to the excessive cutting force, which extends to the underneath of machining surface and forms damage rapidly. For the precise prediction and control of cutting force, we established an artificial neural network cutting force model based on the experimental cutting force data to predict the cutting force change rule in machining CFRP under different fiber orientations, cutting depths and tool angles. Orthogonal cutting experiments on CFRP unidirectional laminate of typical fiber orientation with different tool angles and cutting parameters were conducted to verify the predicting model, and the predicting precision is up to 85%. Combined with the online microscopic prediction results of chip forming process, it is concluded that the fiber orientation is the primary factor affecting the cutting forces of CFRP, as varies from 0° to 135°, chip formation ways include the crushing-dominated failure type and bending failure type; the cutting force firstly decreases and then increases as the fiber orientation angle increases, and is maximum at 135°; the cutting force increases generally as cutting depth increases.
2016, 33(3): 525-534.
doi: 10.13801/j.cnki.fhclxb.20150729.001
Abstract:
A micromechanical numerical model was established for composites, including the interface and taking into account random fiber distribution, to simulate the thermal residual stress of glass fiber/epoxy composites during the curing process. By comparison with the calculation results of model with periodic fiber distribution, it is found that the fiber array form has great influence on the thermal residual stress of composites, with the maximum thermal residual stress of random fiber distribution much greater than that of periodic fiber distribution. The damage and failure process of composites subjected to transverse tension and compression load including thermal residual stress were also investigated. The results indicate that the existence of thermal residual stress significantly affects the damage initiation location and progressing path of composites, weakening the transverse tensile and compressive strength of the composites. Under transverse tension load, after including thermal residual stress, the strength of the composite decreases somewhat, and the fracture strain decreases greatly; under transverse compression load, after including thermal residual stress, the strength of the composite decreases slightly, but the failure strain almost remains unchanged. Due to the effect of thermal residual stress, the transverse tensile and compressive strength of the composites decrease by 10.5% and 5.2%, respectively.
A micromechanical numerical model was established for composites, including the interface and taking into account random fiber distribution, to simulate the thermal residual stress of glass fiber/epoxy composites during the curing process. By comparison with the calculation results of model with periodic fiber distribution, it is found that the fiber array form has great influence on the thermal residual stress of composites, with the maximum thermal residual stress of random fiber distribution much greater than that of periodic fiber distribution. The damage and failure process of composites subjected to transverse tension and compression load including thermal residual stress were also investigated. The results indicate that the existence of thermal residual stress significantly affects the damage initiation location and progressing path of composites, weakening the transverse tensile and compressive strength of the composites. Under transverse tension load, after including thermal residual stress, the strength of the composite decreases somewhat, and the fracture strain decreases greatly; under transverse compression load, after including thermal residual stress, the strength of the composite decreases slightly, but the failure strain almost remains unchanged. Due to the effect of thermal residual stress, the transverse tensile and compressive strength of the composites decrease by 10.5% and 5.2%, respectively.
2016, 33(3): 535-544.
doi: 10.13801/j.cnki.fhclxb.20150709.002
Abstract:
In order to study the effect of hydrothermal environment on the fatigue properties of carbon fiber fabric composite laminates, the tests of carbon fiber fabric on fatigue and residual compressive strength with the center-hole laminates were carried out. For the tests on tension-compression fatigue in hydrothermal environment, a chamber used for hydrothermal environment was designed. In accordance with ASTM standard, the fatigue test fixture and compression test fixture were designed and produced. Then the tension-compression fatigue tests of specimens were carried out in conditions of standard environment conditon (temperature of (23±2)℃, relative humidity of (50±5)% RH) and hydrothermal environment condition (temperature of (70±2)℃, relative humidity of (85±5)% RH). After that, the residual compressive strength tests were carried out, respectively. The residual compressive strength after fatigue in condition of standard environment was set as a reference value, compared with the ultimate compression strength corresponding to the failure load in condition of hydrothermal environment, calculating the difference between them. According to the comparison of test result, it shows that the residual compressive strength of specimens after fatigue in condition of hydrothermal environment decreases by 14%, so the hydrothermal environment has little effect on the residual compressive strength of carbon fiber fabric composite laminate specimens after fatigue under load spectrum.
In order to study the effect of hydrothermal environment on the fatigue properties of carbon fiber fabric composite laminates, the tests of carbon fiber fabric on fatigue and residual compressive strength with the center-hole laminates were carried out. For the tests on tension-compression fatigue in hydrothermal environment, a chamber used for hydrothermal environment was designed. In accordance with ASTM standard, the fatigue test fixture and compression test fixture were designed and produced. Then the tension-compression fatigue tests of specimens were carried out in conditions of standard environment conditon (temperature of (23±2)℃, relative humidity of (50±5)% RH) and hydrothermal environment condition (temperature of (70±2)℃, relative humidity of (85±5)% RH). After that, the residual compressive strength tests were carried out, respectively. The residual compressive strength after fatigue in condition of standard environment was set as a reference value, compared with the ultimate compression strength corresponding to the failure load in condition of hydrothermal environment, calculating the difference between them. According to the comparison of test result, it shows that the residual compressive strength of specimens after fatigue in condition of hydrothermal environment decreases by 14%, so the hydrothermal environment has little effect on the residual compressive strength of carbon fiber fabric composite laminate specimens after fatigue under load spectrum.
2016, 33(3): 545-550.
doi: 10.13801/j.cnki.fhclxb.20150623.002
Abstract:
We presents the low velocity impact mechanical behaviors of 3D orthogonal woven basalt/epoxy woven composites after exposure to 180℃ high temperature environment for different aging time. The load-displacement curves of specimens in process of low velocity impact for different aging time have been obtained. The research indicates that the peak load and the slope of load-displacement curves of 3D orthogonal woven basalt/epoxy composites monotonically decrease with the increase of aging time, while the deflection gradually increases. While with the increasing of impact energy, the peak load, the deflection and the slope of curves for 3D orthogonal woven basalt/epoxy composite specimens with the same aging condition also raise. The SEM observations for the high temperature aged 3D orthogonal woven basalt/epoxy composite specimens indicate the presence of fiber/resin matrix debonding crack, the amount and size of crack increase with increasing aging time.
We presents the low velocity impact mechanical behaviors of 3D orthogonal woven basalt/epoxy woven composites after exposure to 180℃ high temperature environment for different aging time. The load-displacement curves of specimens in process of low velocity impact for different aging time have been obtained. The research indicates that the peak load and the slope of load-displacement curves of 3D orthogonal woven basalt/epoxy composites monotonically decrease with the increase of aging time, while the deflection gradually increases. While with the increasing of impact energy, the peak load, the deflection and the slope of curves for 3D orthogonal woven basalt/epoxy composite specimens with the same aging condition also raise. The SEM observations for the high temperature aged 3D orthogonal woven basalt/epoxy composite specimens indicate the presence of fiber/resin matrix debonding crack, the amount and size of crack increase with increasing aging time.
2016, 33(3): 551-557.
doi: 10.13801/j.cnki.fhclxb.20150709.001
Abstract:
Based on the effective stress principle, Darcy's law and the curvilinear coordinate system, resin flow and fiber compaction control equation of curved laminated composite structures were developed. The laminate simulation model based on AS4/3501-6 fiber resin system was established and the validity of the model was verified by comparing analytical results with experiment data. The research had been carried on the rule about the influence of curvature parameters on the consolidation of composite structures under non-isothermal conditions, and the influence mechanism of the resin flow behavior which was affected by curvature-thickness and curvature-pressure coupling parameters was compared and analyzed. The results show that the curvature parameter of structures can influence the distribution of resin, and the bigger the curvature is, the less uniform the distribution of resin is. The expression of effect of curvature parameter is affected by the parameters of thickness and pressure, and the effect on the curvature is minor when thickness and pressure is small.
Based on the effective stress principle, Darcy's law and the curvilinear coordinate system, resin flow and fiber compaction control equation of curved laminated composite structures were developed. The laminate simulation model based on AS4/3501-6 fiber resin system was established and the validity of the model was verified by comparing analytical results with experiment data. The research had been carried on the rule about the influence of curvature parameters on the consolidation of composite structures under non-isothermal conditions, and the influence mechanism of the resin flow behavior which was affected by curvature-thickness and curvature-pressure coupling parameters was compared and analyzed. The results show that the curvature parameter of structures can influence the distribution of resin, and the bigger the curvature is, the less uniform the distribution of resin is. The expression of effect of curvature parameter is affected by the parameters of thickness and pressure, and the effect on the curvature is minor when thickness and pressure is small.
2016, 33(3): 558-563.
doi: 10.13801/j.cnki.fhclxb.20150528.004
Abstract:
Ag-AlN was prepared by electroless plating with Pd-free activation method and the acrylate adhesive was prepared by solution polymerization method. The Ag-AlN/acrylate electrically conductive adhesives with high thermal conductivity were prepared by ultrasound-assisted solution blending method. The structures of Ag-AlN were characterized by XRD, EDS and SEM etc. The results indicate that after the high temperature and cleaning by acid cleaning fluid, the impurities on surface of AlN is removed and dense Al2O3 layer forms on surface of AlN. The Ag-AlN prepared by electroless plating with Pd-free activation method has good electrical and thermal conductivity. The electrical conductivity of Ag-AlN reaches 7.06×102 S/cm from 10-13 S/cm of AlN and the thermal conductivity reaches 230 W/(m·K) from 170 W/(m·K) of AlN. According to the calculation, the mass fraction of Ag layer on surface of Ag-AlN is 13%, the thickness of Ag layer is about 80 nm, and when the mass fraction of Ag-AlN filler in conductive adhesive is 50%, the electrical conductivity of Ag-AlN/acrylate electrically conductive adhesives is 1.9 S/cm, and thermal conductivity reaches 3.1 W/(m·K).
Ag-AlN was prepared by electroless plating with Pd-free activation method and the acrylate adhesive was prepared by solution polymerization method. The Ag-AlN/acrylate electrically conductive adhesives with high thermal conductivity were prepared by ultrasound-assisted solution blending method. The structures of Ag-AlN were characterized by XRD, EDS and SEM etc. The results indicate that after the high temperature and cleaning by acid cleaning fluid, the impurities on surface of AlN is removed and dense Al2O3 layer forms on surface of AlN. The Ag-AlN prepared by electroless plating with Pd-free activation method has good electrical and thermal conductivity. The electrical conductivity of Ag-AlN reaches 7.06×102 S/cm from 10-13 S/cm of AlN and the thermal conductivity reaches 230 W/(m·K) from 170 W/(m·K) of AlN. According to the calculation, the mass fraction of Ag layer on surface of Ag-AlN is 13%, the thickness of Ag layer is about 80 nm, and when the mass fraction of Ag-AlN filler in conductive adhesive is 50%, the electrical conductivity of Ag-AlN/acrylate electrically conductive adhesives is 1.9 S/cm, and thermal conductivity reaches 3.1 W/(m·K).
2016, 33(3): 564-571.
doi: 10.13801/j.cnki.fhclxb.20150707.001
Abstract:
One dimensional nanoscale CeO2 was prepared, and its specific surface area is larger than that of commercial available CeO2 according to the analysis of scanning electron microscope. In order to prevent the aggregation of CeO2 in fluorosilicone rubber (FSR), KH570 was used to modify the surface of CeO2. Infrared spectrum, thermo-gravimetric and lipophilic degree test were employed to characterize the modification effect. The optimized modification conditions were obtained via orthogonal tests. The unmodified and modified CeO2, as the heat resistant agents, were respectively added into FSR. CeO2/FSR composites show remarkable heat resistance effects. Compared with the blank control, the tensile strength of CeO2/FSR composites increases by 48%, and breaking elongation increases by 36%. Meanwhile, the modified CeO2 could be well dispersed in FSR and has less effect on the virgin performance of FSR.
One dimensional nanoscale CeO2 was prepared, and its specific surface area is larger than that of commercial available CeO2 according to the analysis of scanning electron microscope. In order to prevent the aggregation of CeO2 in fluorosilicone rubber (FSR), KH570 was used to modify the surface of CeO2. Infrared spectrum, thermo-gravimetric and lipophilic degree test were employed to characterize the modification effect. The optimized modification conditions were obtained via orthogonal tests. The unmodified and modified CeO2, as the heat resistant agents, were respectively added into FSR. CeO2/FSR composites show remarkable heat resistance effects. Compared with the blank control, the tensile strength of CeO2/FSR composites increases by 48%, and breaking elongation increases by 36%. Meanwhile, the modified CeO2 could be well dispersed in FSR and has less effect on the virgin performance of FSR.
2016, 33(3): 572-579.
doi: 10.13801/j.cnki.fhclxb.20150715.002
Abstract:
Taking the graphite oxide as the supporter, using sodium lignosulphonate as the dopant and ferric chloride as the oxidant, the polypyrrole(PPy)/graphite oxide composite was prepared by the chemical in-situ polymerization of pyrrole monomer in the graphite oxide layers. The phase composition, structure and morphology were characterized by XRD, FTIR and SEM, respectively. The thermal stability of the composite was analyzed by TGA. The electrochemical performance of the composites was examined through galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance technique. Results show that the PPy/graphite oxide composite synthesized by the chemical in-situ polymerization method is with a kind of "layer-ball" "sandwich" type microstructure so as to form a good conducting network. The synthesized composite is with high crystallinity, neat and less defects. And the pyrrole monomer in the composite materials is bonded with the oxygen containing functional groups of the graphite oxide by the keys of N-H. This kind of novel microstructure modeling of PPy/graphite oxide composite and the perfect chemical key connecting between them confirm it with high capacitance. The specific capacitances of the composites are 500, 460, 427 and 396 F/g at the current density of 0.5, 1.0, 2.0 and 5.0 A/g, respectively. Moreover, after 1000 cycles at the current density of 2.0 A/g, the capacitance retention of the PPy/graphite oxide composite is 97.2%.
Taking the graphite oxide as the supporter, using sodium lignosulphonate as the dopant and ferric chloride as the oxidant, the polypyrrole(PPy)/graphite oxide composite was prepared by the chemical in-situ polymerization of pyrrole monomer in the graphite oxide layers. The phase composition, structure and morphology were characterized by XRD, FTIR and SEM, respectively. The thermal stability of the composite was analyzed by TGA. The electrochemical performance of the composites was examined through galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance technique. Results show that the PPy/graphite oxide composite synthesized by the chemical in-situ polymerization method is with a kind of "layer-ball" "sandwich" type microstructure so as to form a good conducting network. The synthesized composite is with high crystallinity, neat and less defects. And the pyrrole monomer in the composite materials is bonded with the oxygen containing functional groups of the graphite oxide by the keys of N-H. This kind of novel microstructure modeling of PPy/graphite oxide composite and the perfect chemical key connecting between them confirm it with high capacitance. The specific capacitances of the composites are 500, 460, 427 and 396 F/g at the current density of 0.5, 1.0, 2.0 and 5.0 A/g, respectively. Moreover, after 1000 cycles at the current density of 2.0 A/g, the capacitance retention of the PPy/graphite oxide composite is 97.2%.
2016, 33(3): 580-588.
doi: 10.13801/j.cnki.fhclxb.20151013.001
Abstract:
In order to improve the mechanical strength of prototypes fabricated from wood-plastic composite powders by selective laser sintering(SLS) and to design the new composite powders formula applicable to SLS technology, two kinds of wood-plastic composite powders of cellulose/polyether sulfone(PES) and cellulose/polypropylene(PP) were prepared. The systems of cellulose/PES and cellulose/PP blends were blending computed by using the methods of molecular mechanics and molecular dynamics simulation methods. The binding energy distribution curves of cellulose with PES and PP were obtained respectively. By establishing molecular models of cellulose/PES blends with different mass ratios, the Flory-Huggins interaction parameter and static elastic mechanical properties of the models were calculated, and the effect of content of cellulose on the elastic properties of the blends was analyzed. Laser sintering experiments of cellulose/PES and cellulose/PP blends were carried out for verifying the simulation conclusions. The results show that compared with cellulose/PP composite powders, cellulose has the better compatibility with PES, which is suitable for SLS technology. With the addition of 20% to 25% mass fraction of cellulose, the compatibility of the material is at the best condition. The established blend model of cellulose/PES can be used to predict the elastic properties of the fabricated material.
In order to improve the mechanical strength of prototypes fabricated from wood-plastic composite powders by selective laser sintering(SLS) and to design the new composite powders formula applicable to SLS technology, two kinds of wood-plastic composite powders of cellulose/polyether sulfone(PES) and cellulose/polypropylene(PP) were prepared. The systems of cellulose/PES and cellulose/PP blends were blending computed by using the methods of molecular mechanics and molecular dynamics simulation methods. The binding energy distribution curves of cellulose with PES and PP were obtained respectively. By establishing molecular models of cellulose/PES blends with different mass ratios, the Flory-Huggins interaction parameter and static elastic mechanical properties of the models were calculated, and the effect of content of cellulose on the elastic properties of the blends was analyzed. Laser sintering experiments of cellulose/PES and cellulose/PP blends were carried out for verifying the simulation conclusions. The results show that compared with cellulose/PP composite powders, cellulose has the better compatibility with PES, which is suitable for SLS technology. With the addition of 20% to 25% mass fraction of cellulose, the compatibility of the material is at the best condition. The established blend model of cellulose/PES can be used to predict the elastic properties of the fabricated material.
2016, 33(3): 589-596.
doi: 10.13801/j.cnki.fhclxb.20150715.003
Abstract:
The influence and mechanism of fitting modes including clearance and interference on joint stiffness were researched as far as single-bolt, single-lap composite bolted joint was concerned. The validation of the adopted finite element method was confirmed by comparing with the results of tests. The results illustrate that for single-bolt, single-lap composite bolted joint, clearance fit reduces joint stiffness and the joint stiffness decreases almost linearly as clearance increases, clearance fit of 3% bolt diameter decreases joint stiffness by 16%-17%. For joint without hole delamination damage during assembling process, interference fit of 0.5% bolt diameter increases joint stiffness by about 15%. With different fitting modes, the contact stress peak direction and the uneven degree of contact stress distribution through thickness are distinct, which influence the joint stiffness.
The influence and mechanism of fitting modes including clearance and interference on joint stiffness were researched as far as single-bolt, single-lap composite bolted joint was concerned. The validation of the adopted finite element method was confirmed by comparing with the results of tests. The results illustrate that for single-bolt, single-lap composite bolted joint, clearance fit reduces joint stiffness and the joint stiffness decreases almost linearly as clearance increases, clearance fit of 3% bolt diameter decreases joint stiffness by 16%-17%. For joint without hole delamination damage during assembling process, interference fit of 0.5% bolt diameter increases joint stiffness by about 15%. With different fitting modes, the contact stress peak direction and the uneven degree of contact stress distribution through thickness are distinct, which influence the joint stiffness.
2016, 33(3): 597-605.
doi: 10.13801/j.cnki.fhclxb.20151008.001
Abstract:
Concrete with nano-Fe2O3 (NF), double kinds of nanomaterials (nano-Fe2O3 and nano-CaCO3, NFC), and three kinds of nanomaterials (nano-Fe2O3, nano-CaCO3, nano-SiO2, NFCS) all containing the addition of 2.0% (based on cement quality)were prepared, then the dynamic properties of three kinds of concrete were compared with the plain concrete (PC) under varied average strain rate levels by the 100 mm-diameter split Hopkinson pressure bar (SHPB) test device after a 28 d maintenance period. The results show that the addition of composite nanomaterials can effectively improve the compressive strength of concrete under quasi static load. Under impact load, NFC has the highest dynamic compressive strength at middle and low average strain rate, it is 31.6% higher than that of PC at 80 s-1. Dynamic compressive strength of NF has an advantage at high level of average strain rate with 16% higher than that of PC at the average strain rate of 125 s-1. Peak strain of NF has significant advantages under impact load, which verified good deformation performance; From the perspective of the evaluation index of specific energy absorption, NF increases by 66.6% and 75.7% than that of PC at the average strain rate of 75 s-1and 125 s-1. SEM photograph analysis shows that nano-Fe2O3 particles increases the compactness of cement stone, improves the strength and toughness of NF. Mercury injection test analysis show that nanoparticles CaCO3 improve the pore structure of cement stone in concrete.
Concrete with nano-Fe2O3 (NF), double kinds of nanomaterials (nano-Fe2O3 and nano-CaCO3, NFC), and three kinds of nanomaterials (nano-Fe2O3, nano-CaCO3, nano-SiO2, NFCS) all containing the addition of 2.0% (based on cement quality)were prepared, then the dynamic properties of three kinds of concrete were compared with the plain concrete (PC) under varied average strain rate levels by the 100 mm-diameter split Hopkinson pressure bar (SHPB) test device after a 28 d maintenance period. The results show that the addition of composite nanomaterials can effectively improve the compressive strength of concrete under quasi static load. Under impact load, NFC has the highest dynamic compressive strength at middle and low average strain rate, it is 31.6% higher than that of PC at 80 s-1. Dynamic compressive strength of NF has an advantage at high level of average strain rate with 16% higher than that of PC at the average strain rate of 125 s-1. Peak strain of NF has significant advantages under impact load, which verified good deformation performance; From the perspective of the evaluation index of specific energy absorption, NF increases by 66.6% and 75.7% than that of PC at the average strain rate of 75 s-1and 125 s-1. SEM photograph analysis shows that nano-Fe2O3 particles increases the compactness of cement stone, improves the strength and toughness of NF. Mercury injection test analysis show that nanoparticles CaCO3 improve the pore structure of cement stone in concrete.
2016, 33(3): 606-612.
doi: 10.13801/j.cnki.fhclxb.20150921.001
Abstract:
A continuum damage constitutive model of 2.5D C/SiC composites containing both tensile and shear damage variables were established based on continuum damage mechanics. Tensile and shear tests were conducted to obtain the stress-strain curves, and the test curves were fitted to obtain parameters of damage variable evolution. The constitutive model was then embedded into commercial finite element software ANSYS by subroutine technology and the finite element method was used to calculate the stress-strain curves of materials. The coupling effect of tensile and shear damage was considered. The stress-strain curves under off-axis tensile condition was calculated. The results show that the stress-strain curves along warp and weft direction tensile and in-plane shear agree well with the test results and the maximum deviation are respectively 4.30%, 3.09% and 3.73%; the calculated off-axis tensile stress-strain curve is also consistent with the test data.
A continuum damage constitutive model of 2.5D C/SiC composites containing both tensile and shear damage variables were established based on continuum damage mechanics. Tensile and shear tests were conducted to obtain the stress-strain curves, and the test curves were fitted to obtain parameters of damage variable evolution. The constitutive model was then embedded into commercial finite element software ANSYS by subroutine technology and the finite element method was used to calculate the stress-strain curves of materials. The coupling effect of tensile and shear damage was considered. The stress-strain curves under off-axis tensile condition was calculated. The results show that the stress-strain curves along warp and weft direction tensile and in-plane shear agree well with the test results and the maximum deviation are respectively 4.30%, 3.09% and 3.73%; the calculated off-axis tensile stress-strain curve is also consistent with the test data.
2016, 33(3): 613-617.
doi: 10.13801/j.cnki.fhclxb.20150611.001
Abstract:
In order to prepare efficient absorbent for Cd(Ⅱ), polymeric aluminum hydroxyl (Al13) was added into the dispersion of graphite oxide (GO) by direct titration method firstly, and graphite oxide-polymeric aluminum hydroxyl composites (GO-Al13) were synthesized using GO as the matrix. Then, analysis technology such as XRD, FTIR, SEM and so on were used to characterize GO-Al13, and 10 mg GO-Al13 was added into 50 mL Cd(Ⅱ) waste water whose initial concentration was 10 mg/L to conduct the adsorption experiments, thus the removal effects of GO-Al13 on Cd(Ⅱ) were investigated. The results show that [Al13]7+ ions will react with oxygen-containing functional groups of GO to form Al-O groups. After adding [Al13]7+ ions into GO, the surface morphologies of GO-Al13 will change a lot comparing with GO, irregular concave-convex structures emerge and roughness increases significantly. When the initial concentration of Cd(Ⅱ) in waste water is 10 mg/L and initial pH is 6.0, the removal rate can reach 98.92%. The conclusions obtained indicate that the removal effects of GO-Al13 for Cd(Ⅱ) is preferable.
In order to prepare efficient absorbent for Cd(Ⅱ), polymeric aluminum hydroxyl (Al13) was added into the dispersion of graphite oxide (GO) by direct titration method firstly, and graphite oxide-polymeric aluminum hydroxyl composites (GO-Al13) were synthesized using GO as the matrix. Then, analysis technology such as XRD, FTIR, SEM and so on were used to characterize GO-Al13, and 10 mg GO-Al13 was added into 50 mL Cd(Ⅱ) waste water whose initial concentration was 10 mg/L to conduct the adsorption experiments, thus the removal effects of GO-Al13 on Cd(Ⅱ) were investigated. The results show that [Al13]7+ ions will react with oxygen-containing functional groups of GO to form Al-O groups. After adding [Al13]7+ ions into GO, the surface morphologies of GO-Al13 will change a lot comparing with GO, irregular concave-convex structures emerge and roughness increases significantly. When the initial concentration of Cd(Ⅱ) in waste water is 10 mg/L and initial pH is 6.0, the removal rate can reach 98.92%. The conclusions obtained indicate that the removal effects of GO-Al13 for Cd(Ⅱ) is preferable.
2016, 33(3): 618-627.
doi: 10.13801/j.cnki.fhclxb.20150907.001
Abstract:
Firstly, TiC0.5N0.5/Si3N4 composite ceramics were prepared by hot-pressing method using 15vol% or 25vol% TiC0.5N0.5 powders as conducting second phase. Then, CrAlN and TiN/Al2O3/TiN coatings were deposited on the surfaces of TiC0.5N0.5/Si3N4 ceramic tools by physical vapor deposition (PVD) and chemical vapor deposition (CVD) technologies, respectively. Finally, the effects of TiC0.5N0.5 content and coating type on tool wear characteristics were investigated by conducting continuous cutting experiments for gray cast iron on TiC0.5N0.5/Si3N4 tools, and the wear mechanisms of tools were also discussed. The results show that the increasing of TiC0.5N0.5 content is beneficial to enhance the matrix hardness and conductivity of TiC0.5N0.5/Si3N4 composite ceramic tools, but has little effect on wear resistance and cutting length. When depositing CrAlN coating by PVD technology, with TiC0.5N0.5 content increasing, the thickness, adhesion strength and hardness of coating increase, the wear performances of coated tools enhance significantly, and cutting length extends obviously. However, when depositing TiN/Al2O3/TiN coating by CVD technology, the variation of TiC0.5N0.5 content almost has no effects on coating thickness, adhesion strength and hardness, as well as the comprehensive cutting performances of TiN/Al2O3/TiN coated tools change little. Both of CrAlN coating and TiN/Al2O3/TiN coating can improve the wear resistance and cutting length of TiC0.5N0.5/Si3N4 composite ceramic tools significantly. Compared with TiN/Al2O3/TiN coating, CrAlN coating has higher coating hardness and adhesion strength; while TiN/Al2O3/TiN coated tool shows more excellent wear resistance and cutting length for TiN/Al2O3/TiN coating has larger coating thickness. The main wear mechanism of TiC0.5N0.5/Si3N4 composite ceramic tools is abrasive wear caused by mechanical friction, and associated with a small amount of adhesive wear.
Firstly, TiC0.5N0.5/Si3N4 composite ceramics were prepared by hot-pressing method using 15vol% or 25vol% TiC0.5N0.5 powders as conducting second phase. Then, CrAlN and TiN/Al2O3/TiN coatings were deposited on the surfaces of TiC0.5N0.5/Si3N4 ceramic tools by physical vapor deposition (PVD) and chemical vapor deposition (CVD) technologies, respectively. Finally, the effects of TiC0.5N0.5 content and coating type on tool wear characteristics were investigated by conducting continuous cutting experiments for gray cast iron on TiC0.5N0.5/Si3N4 tools, and the wear mechanisms of tools were also discussed. The results show that the increasing of TiC0.5N0.5 content is beneficial to enhance the matrix hardness and conductivity of TiC0.5N0.5/Si3N4 composite ceramic tools, but has little effect on wear resistance and cutting length. When depositing CrAlN coating by PVD technology, with TiC0.5N0.5 content increasing, the thickness, adhesion strength and hardness of coating increase, the wear performances of coated tools enhance significantly, and cutting length extends obviously. However, when depositing TiN/Al2O3/TiN coating by CVD technology, the variation of TiC0.5N0.5 content almost has no effects on coating thickness, adhesion strength and hardness, as well as the comprehensive cutting performances of TiN/Al2O3/TiN coated tools change little. Both of CrAlN coating and TiN/Al2O3/TiN coating can improve the wear resistance and cutting length of TiC0.5N0.5/Si3N4 composite ceramic tools significantly. Compared with TiN/Al2O3/TiN coating, CrAlN coating has higher coating hardness and adhesion strength; while TiN/Al2O3/TiN coated tool shows more excellent wear resistance and cutting length for TiN/Al2O3/TiN coating has larger coating thickness. The main wear mechanism of TiC0.5N0.5/Si3N4 composite ceramic tools is abrasive wear caused by mechanical friction, and associated with a small amount of adhesive wear.
2016, 33(3): 628-634.
doi: 10.13801/j.cnki.fhclxb.20150707.002
Abstract:
In order to extend the application area of piezoelectric composites, 0-3 type polyvinylidene fluoride (PVDF)/Pb(Zn1/3Nb2/3)0.05Zr0.47Ti0.48O3 (PZNZT) piezoelectric composites were prepared using solid reaction process firstly. Then, the effects of PVDF content on the phase, microstructures and properties of PVDF/PZNZT composites were investigated. The results show that the average particle size of PZNZT ceramic powders after mixing with PVDF powders is close to that of pure PVDF powders. After sintering under 220℃, the diffraction peaks of PZNZT perovskite structure present in the XRD patterns of PVDF/PZNZT composites mainly. When PVDF content is lower, the combinations between PZNZT ceramic grains are relatively loose; with PVDF content increasing, the ceramic grains are almost surrounded by PVDF phase. The PVDF/PZNZT composites with different PVDF contents present different series and parallel circuits in polarization electric field for the different microstructures. After polarization, the electric-properties of 5wt% PVDF/PZNZT composite are the best, the dielectric constant is 116, dielectric loss tan δ is 0.04, piezoelectric constant is 48 pC/N and electromechanical coupling coefficient is 0.28. With PVDF content increasing, the Curie temperature of PVDF/PZNZT composite decreases, and the Vickers hardness increases, but still smaller than the hardness of pure PZNZT piezoelectric ceramic. The conclusions obtained show that the properties of PVDF/PZNZT piezoelectric composites can meet the requirements of underwater acoustic, electroacoustic and ultrasonic transducers et al.
In order to extend the application area of piezoelectric composites, 0-3 type polyvinylidene fluoride (PVDF)/Pb(Zn1/3Nb2/3)0.05Zr0.47Ti0.48O3 (PZNZT) piezoelectric composites were prepared using solid reaction process firstly. Then, the effects of PVDF content on the phase, microstructures and properties of PVDF/PZNZT composites were investigated. The results show that the average particle size of PZNZT ceramic powders after mixing with PVDF powders is close to that of pure PVDF powders. After sintering under 220℃, the diffraction peaks of PZNZT perovskite structure present in the XRD patterns of PVDF/PZNZT composites mainly. When PVDF content is lower, the combinations between PZNZT ceramic grains are relatively loose; with PVDF content increasing, the ceramic grains are almost surrounded by PVDF phase. The PVDF/PZNZT composites with different PVDF contents present different series and parallel circuits in polarization electric field for the different microstructures. After polarization, the electric-properties of 5wt% PVDF/PZNZT composite are the best, the dielectric constant is 116, dielectric loss tan δ is 0.04, piezoelectric constant is 48 pC/N and electromechanical coupling coefficient is 0.28. With PVDF content increasing, the Curie temperature of PVDF/PZNZT composite decreases, and the Vickers hardness increases, but still smaller than the hardness of pure PZNZT piezoelectric ceramic. The conclusions obtained show that the properties of PVDF/PZNZT piezoelectric composites can meet the requirements of underwater acoustic, electroacoustic and ultrasonic transducers et al.
2016, 33(3): 635-642.
doi: 10.13801/j.cnki.fhclxb.20150723.002
Abstract:
A P(GMA-co-HEMA)/SiO2 macroporous composite was synthesized by in-situ polymerization followed by solvent evaporation via a large-sized macroporous SiO2 material as substrate and glycidyl methacrylate(GMA), 2-hydroxyethyl methacrylate(HEMA) as the functional monomers. Samples were characterized by SEM, EDS, BET, FTIR and TG-DTA. The P(GMA-co-HEMA)/SiO2 macroporous composite was employed as support for the immobilization of lipase from Candida rugose (CRL). The results show that the strong capillarity effect of the macroporous SiO2 material makes the copolymer coating on its pore wall uniformly, forming the P(GMA-co-HEMA)/SiO2 composite nano-film. The loading amount and the hydrophilicity of the copolymer can be adjusted by changing the concentration of the monomers and the volume ratio of the monomers, respectively. When the volume concentration of monomers is 10% and the volume ratio of GMA to HEMA is 9∶1, the immobilized lipase reaches its highest specific activity of 3 886.9 U/g and remains 68.7% of its initial activity after 8 consecutive batches of reaction with the substrate.
A P(GMA-co-HEMA)/SiO2 macroporous composite was synthesized by in-situ polymerization followed by solvent evaporation via a large-sized macroporous SiO2 material as substrate and glycidyl methacrylate(GMA), 2-hydroxyethyl methacrylate(HEMA) as the functional monomers. Samples were characterized by SEM, EDS, BET, FTIR and TG-DTA. The P(GMA-co-HEMA)/SiO2 macroporous composite was employed as support for the immobilization of lipase from Candida rugose (CRL). The results show that the strong capillarity effect of the macroporous SiO2 material makes the copolymer coating on its pore wall uniformly, forming the P(GMA-co-HEMA)/SiO2 composite nano-film. The loading amount and the hydrophilicity of the copolymer can be adjusted by changing the concentration of the monomers and the volume ratio of the monomers, respectively. When the volume concentration of monomers is 10% and the volume ratio of GMA to HEMA is 9∶1, the immobilized lipase reaches its highest specific activity of 3 886.9 U/g and remains 68.7% of its initial activity after 8 consecutive batches of reaction with the substrate.
2016, 33(3): 643-649.
doi: 10.13801/j.cnki.fhclxb.20150706.002
Abstract:
The structure strength of cracked metal plates can be greatly improved with the help of bonded composite patches. However, the existence of crack in cracked plates will lead to serious stress concentration phenomenon and produce plastic deformation easily, which shows strong material physics nonlinear characteristics. It is necessary to use elastic and plastic mechanical principle to predict the static strength of the repaired structure bonded with composite patches. Considering the material nonlinearities of the metal plate materials, the elastic-plastic finite element model of the cracked metal plates bonded with composite patches was established, which was validated by test results. On the basis, a method predicting tensile strength was proposed based on crack opening displacement (COD) theory in crack tip, and the plastic deformation, COD of the repaired structure and static tensile strength were analyzed. Results show that, compared with the stress intensity factor K theory, the COD theory can give more precise result in predicting the static tensile strength of the repaired specimen.
The structure strength of cracked metal plates can be greatly improved with the help of bonded composite patches. However, the existence of crack in cracked plates will lead to serious stress concentration phenomenon and produce plastic deformation easily, which shows strong material physics nonlinear characteristics. It is necessary to use elastic and plastic mechanical principle to predict the static strength of the repaired structure bonded with composite patches. Considering the material nonlinearities of the metal plate materials, the elastic-plastic finite element model of the cracked metal plates bonded with composite patches was established, which was validated by test results. On the basis, a method predicting tensile strength was proposed based on crack opening displacement (COD) theory in crack tip, and the plastic deformation, COD of the repaired structure and static tensile strength were analyzed. Results show that, compared with the stress intensity factor K theory, the COD theory can give more precise result in predicting the static tensile strength of the repaired specimen.
2016, 33(3): 650-656.
doi: 10.13801/j.cnki.fhclxb.20150703.001
Abstract:
In order to improve the reliability and load carrying capacity of bolted joint laminate structure, the multi-scale numerical model combining with improved cells model and considering the failure of constituent materials was created based on ABAQUS software and user subroutine (USDFLD). Based on the model, the mechanical properties of the double-shear single bolted joint laminate structures was characterized, and the effects of layup form and geometry on the properties of bolted joint structure were researched. The predicted results using the model were in good agreement with the testing results. The results show that the bearing strength of quasi-isotropic bolted joint laminate structure was higher than that of orthotropic bolted joint laminate structure, and the failure mode of the former was bearing failure, but that of the latter was shearing failure. The shearing failure will result in the decrease of structure bearing capacity. So it should be avoided during the design. When the ratio of edge to diameter for laminate is greater than 3, the bearing strength converges to a stable value for the bolted joint structure with different ratio of width to diameter. But as for the bolted joint structure with the same ratio of edge to diameter, the bearing strength increases with the increase of the ratio of width to diameter. It also should be given consideration during the process of bolted joint structure design.
In order to improve the reliability and load carrying capacity of bolted joint laminate structure, the multi-scale numerical model combining with improved cells model and considering the failure of constituent materials was created based on ABAQUS software and user subroutine (USDFLD). Based on the model, the mechanical properties of the double-shear single bolted joint laminate structures was characterized, and the effects of layup form and geometry on the properties of bolted joint structure were researched. The predicted results using the model were in good agreement with the testing results. The results show that the bearing strength of quasi-isotropic bolted joint laminate structure was higher than that of orthotropic bolted joint laminate structure, and the failure mode of the former was bearing failure, but that of the latter was shearing failure. The shearing failure will result in the decrease of structure bearing capacity. So it should be avoided during the design. When the ratio of edge to diameter for laminate is greater than 3, the bearing strength converges to a stable value for the bolted joint structure with different ratio of width to diameter. But as for the bolted joint structure with the same ratio of edge to diameter, the bearing strength increases with the increase of the ratio of width to diameter. It also should be given consideration during the process of bolted joint structure design.
2016, 33(3): 657-665.
doi: 10.13801/j.cnki.fhclxb.20150615.002
Abstract:
During the long-term natural evolution, the scales of teleost fish become ultra-thin and ultralight, and have excellent flexibility. In order to develop an innovative flexible protection system, the hierarchical structure and mechanical properties of scales from grass carp were investigated. Two types of samples for scales and collagen layers were extracted from the central regions of scales by three different orientations (0°, 45° and 90°) firstly. Then, tensile tests in uniaxial were conducted and mechanical properties of scales with different water contents as well as scales and collagen layers under different strain rates were investigated comparatively. The result shows that the scales of grass carp consist of outer hard bony layer and inner soft collagen layer, and the collagen layer consists of twisted overplayed collagenous fiber lamellas whose spiral angles are about 28°-31°. The mechanical properties of scale are in-plain anisotropic, while the mechanical properties of collagen layer are isotropic. The elastic modulus and tensile strength of dehydrated scale increase significantly, which are about 10 times and 3 times of those of hydrated scale, while the ultimate strain reduces by about 50%. The mechanical properties of hydrated scale and collagen layer are highly dependent on strain rate. The conclusions obtained provide ideas for the investigation of bio-inspired innovative composites and flexible protection systems.
During the long-term natural evolution, the scales of teleost fish become ultra-thin and ultralight, and have excellent flexibility. In order to develop an innovative flexible protection system, the hierarchical structure and mechanical properties of scales from grass carp were investigated. Two types of samples for scales and collagen layers were extracted from the central regions of scales by three different orientations (0°, 45° and 90°) firstly. Then, tensile tests in uniaxial were conducted and mechanical properties of scales with different water contents as well as scales and collagen layers under different strain rates were investigated comparatively. The result shows that the scales of grass carp consist of outer hard bony layer and inner soft collagen layer, and the collagen layer consists of twisted overplayed collagenous fiber lamellas whose spiral angles are about 28°-31°. The mechanical properties of scale are in-plain anisotropic, while the mechanical properties of collagen layer are isotropic. The elastic modulus and tensile strength of dehydrated scale increase significantly, which are about 10 times and 3 times of those of hydrated scale, while the ultimate strain reduces by about 50%. The mechanical properties of hydrated scale and collagen layer are highly dependent on strain rate. The conclusions obtained provide ideas for the investigation of bio-inspired innovative composites and flexible protection systems.
2016, 33(3): 666-674.
doi: 10.13801/j.cnki.fhclxb.20150910.001
Abstract:
The off-axis elastic constants theory for composites was applied in the Hedgepeth's model to make the model workable for all cracks with inclined orientations. Then, according to the Griffith energy theory and the test phenomena, a theoretical formula was derived to evaluate the tearing strength of envelope materials with central cracks. The results demonstrate that the tearing strengths are affected by the internal factors (such as the elastic constants, weaving density, etc) and external factors (such as the inclined orientation, crack length, etc). Furthermore, the precision and applicability of the formula were verified with the test result and the other tearing strength theories. Investigations on the tearing strength of envelope materials will provide significant guidance for the strength design and safety assessment of airship structures.
The off-axis elastic constants theory for composites was applied in the Hedgepeth's model to make the model workable for all cracks with inclined orientations. Then, according to the Griffith energy theory and the test phenomena, a theoretical formula was derived to evaluate the tearing strength of envelope materials with central cracks. The results demonstrate that the tearing strengths are affected by the internal factors (such as the elastic constants, weaving density, etc) and external factors (such as the inclined orientation, crack length, etc). Furthermore, the precision and applicability of the formula were verified with the test result and the other tearing strength theories. Investigations on the tearing strength of envelope materials will provide significant guidance for the strength design and safety assessment of airship structures.
2016, 33(3): 675-680.
doi: 10.13801/j.cnki.fhclxb.20150911.001
Abstract:
In order to enhance the mechanical behavior of ultra-light lattice composite structure with high strength, especially its anti-buckling ability, a new hierarchical isogrid sandwich structure was designed. An equivalent continuum method was proposed to put forward the equivalent calculation theory of hierarchical isogrid sandwich plate and to predict the effective elastic modulus and bending rigidity of the stretching-dominated hierarchical structure. Elastic buckling failure load and strength in material failure mode of the hierarchical isogrid sandwich plate in edgewise compression were analyzed. Based on these theoretical models, failure mode map of the hierarchical isogrid sandwich plate under edgewise compression was plotted to point out the corresponding relationships between the structure failure modes and the dimensions of the hierarchical isogrid sandwich plate. Results show that hierarchical isogrid sandwich plate with I-shaped cross-section is stiffer and stronger in buckling resistance compared with isogrid plate with traditional rectangular cross-section. The property of hierarchical isogrid sandwich plate is superior as a kind of ultra-light lattice structure with high strength.
In order to enhance the mechanical behavior of ultra-light lattice composite structure with high strength, especially its anti-buckling ability, a new hierarchical isogrid sandwich structure was designed. An equivalent continuum method was proposed to put forward the equivalent calculation theory of hierarchical isogrid sandwich plate and to predict the effective elastic modulus and bending rigidity of the stretching-dominated hierarchical structure. Elastic buckling failure load and strength in material failure mode of the hierarchical isogrid sandwich plate in edgewise compression were analyzed. Based on these theoretical models, failure mode map of the hierarchical isogrid sandwich plate under edgewise compression was plotted to point out the corresponding relationships between the structure failure modes and the dimensions of the hierarchical isogrid sandwich plate. Results show that hierarchical isogrid sandwich plate with I-shaped cross-section is stiffer and stronger in buckling resistance compared with isogrid plate with traditional rectangular cross-section. The property of hierarchical isogrid sandwich plate is superior as a kind of ultra-light lattice structure with high strength.
2016, 33(3): 681-688.
doi: 10.13801/j.cnki.fhclxb.20151013.004
Abstract:
Two-dimensional plane strain models were used to analyze the failure of stitched specimens. The interface failure condition was simulated with cohesive zone model, and the reinforcement effect of stitching was simulated with nonlinear spring elements inserted into the upper and lower interface of layer. The mechanical properties of the nonlinear spring elements (bridging law) were obtained based on micromechanical approach. The finite element analysis results agree well with test data. Based on the verified finite element model, the parametric analysis of stitching reinforcement in the flange area was done and parameters include the material, diameter of the stitch and density of stitching. The effects of parameters on pull-off carrying capacity of T-joint were studied. Results show that stitching can effectively improve the pull-off load capacity of T-joints and make the load capacity remain high under a large loading displacement. The pull-off load capacity of the T-joint increases as the diameter of stitch and density of stitching increase, and the influences of diameter and density are significant. The tensile strength of stitch is the main factor that affects the property of stitch and the pull-off strength of T-joint increases as the tensile strength of stitch increases, while the pull-off strength of T-joint increases as the tensile modulus of stitch decreases, but the influence of tensile modulus is not that significant of tensile strength.
Two-dimensional plane strain models were used to analyze the failure of stitched specimens. The interface failure condition was simulated with cohesive zone model, and the reinforcement effect of stitching was simulated with nonlinear spring elements inserted into the upper and lower interface of layer. The mechanical properties of the nonlinear spring elements (bridging law) were obtained based on micromechanical approach. The finite element analysis results agree well with test data. Based on the verified finite element model, the parametric analysis of stitching reinforcement in the flange area was done and parameters include the material, diameter of the stitch and density of stitching. The effects of parameters on pull-off carrying capacity of T-joint were studied. Results show that stitching can effectively improve the pull-off load capacity of T-joints and make the load capacity remain high under a large loading displacement. The pull-off load capacity of the T-joint increases as the diameter of stitch and density of stitching increase, and the influences of diameter and density are significant. The tensile strength of stitch is the main factor that affects the property of stitch and the pull-off strength of T-joint increases as the tensile strength of stitch increases, while the pull-off strength of T-joint increases as the tensile modulus of stitch decreases, but the influence of tensile modulus is not that significant of tensile strength.
