2016 Vol. 33, No. 12
2016, 33(12): 2699-2705.
doi: 10.13801/j.cnki.fhclxb.20160120.001
Abstract:
The high-temperature mechanical properties of carbon fiber reinforced polyimide resin matrix MT300/KH420 composites were studied both in macro and micro scale, during which the flexural property variation rule for MT300/KH420 composites of laminates with ply orientation of [0°]14 and[±45°/0°/90°/+45°/0°2]s were especially analyzed at temperature ranging from ambient temperature to 500℃. Research shows that MT300/KH420 composite has good mechanical property at high temperature. The flexural strength of [0°]14 laminates exhibit a 51% retention at 420℃, while at 500℃ it changes little. At ambient temperature,[0°]14 laminates exhibit brittle fractures with a rough facture surface and crack growth direction along thickness. As temperature rises, resin tends to have a stronger flowability, leading to a viscoelastic behavior, while failure mainly occurs at the loading nose. At 500℃, thermal exposure has caused the decomposition of resin matrix, leaving separations between the bundles of the oxidated fibers. As for[±45°/0°/90°/+45°/0°2]s laminates, the flexural properties show a more stable retention at high temperature. Crack along 45° direction at outer surfaces as well as interlamination are the main failure modes. At 500℃, a severe delamination happens. Compared with matrix-dominated laminates, the flexural properties of fiber-dominated ones are less dependent on temperature.
The high-temperature mechanical properties of carbon fiber reinforced polyimide resin matrix MT300/KH420 composites were studied both in macro and micro scale, during which the flexural property variation rule for MT300/KH420 composites of laminates with ply orientation of [0°]14 and[±45°/0°/90°/+45°/0°2]s were especially analyzed at temperature ranging from ambient temperature to 500℃. Research shows that MT300/KH420 composite has good mechanical property at high temperature. The flexural strength of [0°]14 laminates exhibit a 51% retention at 420℃, while at 500℃ it changes little. At ambient temperature,[0°]14 laminates exhibit brittle fractures with a rough facture surface and crack growth direction along thickness. As temperature rises, resin tends to have a stronger flowability, leading to a viscoelastic behavior, while failure mainly occurs at the loading nose. At 500℃, thermal exposure has caused the decomposition of resin matrix, leaving separations between the bundles of the oxidated fibers. As for[±45°/0°/90°/+45°/0°2]s laminates, the flexural properties show a more stable retention at high temperature. Crack along 45° direction at outer surfaces as well as interlamination are the main failure modes. At 500℃, a severe delamination happens. Compared with matrix-dominated laminates, the flexural properties of fiber-dominated ones are less dependent on temperature.
2016, 33(12): 2706-2711.
doi: 10.13801/j.cnki.fhclxb.20160125.001
Abstract:
The hydroxylated multi-walled carbon tubes (MWCNTs) was synthesized by surface-modification of MWCNTs. The MWCNTs grafted poly (caprolactone) (PCL) based macroinitiator was obtained by the ring opening polymerization of caprolactone which was catalyzed by MWCNTs-OH and further treated with 2-bromoisobutyryl bromide. The MWCNTs/PCL-b-PNIPAM composite was prepared by in situ atom transfer radical polymerization (ATRP). The products were characterized by FTIR, TGA, XRD, NMR and TEM. The crystallization property and miscibility of MWCNTs/PCL-b-PNIPAM composites in chloroform solvent were observed. The XRD results show that the crystallization peak of MWCNTs/PCL-b-PNIPAM composites is similar to the PCL-b-PNIPAM block copolymer, and MWCNTs/PCL-b-PNIPAM composites have a good miscibility in chloroform solution.
The hydroxylated multi-walled carbon tubes (MWCNTs) was synthesized by surface-modification of MWCNTs. The MWCNTs grafted poly (caprolactone) (PCL) based macroinitiator was obtained by the ring opening polymerization of caprolactone which was catalyzed by MWCNTs-OH and further treated with 2-bromoisobutyryl bromide. The MWCNTs/PCL-b-PNIPAM composite was prepared by in situ atom transfer radical polymerization (ATRP). The products were characterized by FTIR, TGA, XRD, NMR and TEM. The crystallization property and miscibility of MWCNTs/PCL-b-PNIPAM composites in chloroform solvent were observed. The XRD results show that the crystallization peak of MWCNTs/PCL-b-PNIPAM composites is similar to the PCL-b-PNIPAM block copolymer, and MWCNTs/PCL-b-PNIPAM composites have a good miscibility in chloroform solution.
2016, 33(12): 2712-2717.
doi: 10.13801/j.cnki.fhclxb.20160128.001
Abstract:
The dielectric constant of human skin and air have a large mismatch. The materials used for wearable devices need to have a great matching performance with human shin, which can not be achieved by solo material and structure. By using the in-situ polymerization method, a series of barium titanate (BaTiO3)/polyimide(PI) mixed solutions were synthesized. Then, by means of casting method step by step, a multilayer BaTiO3/PI composite film with impedance gradient was designed and fabricated. The results show that BaTiO3 nano-particles can distribute in the composite film uniformly. By adjusting the content of inorganic particles, the dielectric constant of prepared BaTiO3/PI composite film can be controlled in the range of 2.5-34.0. Besides, BaTiO3/PI composite film is insensible to the frequency of electric field and also has a good mechanical property, which can meet the requirements of wearable device materials.
The dielectric constant of human skin and air have a large mismatch. The materials used for wearable devices need to have a great matching performance with human shin, which can not be achieved by solo material and structure. By using the in-situ polymerization method, a series of barium titanate (BaTiO3)/polyimide(PI) mixed solutions were synthesized. Then, by means of casting method step by step, a multilayer BaTiO3/PI composite film with impedance gradient was designed and fabricated. The results show that BaTiO3 nano-particles can distribute in the composite film uniformly. By adjusting the content of inorganic particles, the dielectric constant of prepared BaTiO3/PI composite film can be controlled in the range of 2.5-34.0. Besides, BaTiO3/PI composite film is insensible to the frequency of electric field and also has a good mechanical property, which can meet the requirements of wearable device materials.
2016, 33(12): 2718-2724.
doi: 10.13801/j.cnki.fhclxb.20160219.005
Abstract:
Poly (lactic acid) (PLA) graft copolymer (mPLA) was prepared by graft copolymerization using maleic anhydride and butyl acrylate as comonomers. Then the mPLA was used as compatibilizer to prepare cellulose nanocrystal (NCC)/PLA composites by solution casting method. Effects of mPLA on the structure and properties of NCC/PLA composites were investigated by SEM, DSC, TG, wide angle X-ray diffraction(WXRD), mechanical testing and degradation property test. Results show that the application of mPLA in NCC/PLA composites improves compatibilization between NCC and PLA, and promotes dispersion of NCC in the PLA matrix. More finely dispersed NCC enhances the crystallization nucleation of PLA, resulting in lower crystallization temperature and higher crystallinity. Mechanical properties of NCC/mPLA/PLA composite increase then decrease with increasing mPLA content, when the content of mPLA is 8%, the tensile strength and elastic modulus increase about 30.2% and 41.4% respectively in comparison with those of composite without mPLA. The hydrophilic NCC accelerates degradation of NCC/PLA composite, when mPLA is added, the degradation rate of NCC/PLA composite slowes down but is still higher than that of pure PLA.
Poly (lactic acid) (PLA) graft copolymer (mPLA) was prepared by graft copolymerization using maleic anhydride and butyl acrylate as comonomers. Then the mPLA was used as compatibilizer to prepare cellulose nanocrystal (NCC)/PLA composites by solution casting method. Effects of mPLA on the structure and properties of NCC/PLA composites were investigated by SEM, DSC, TG, wide angle X-ray diffraction(WXRD), mechanical testing and degradation property test. Results show that the application of mPLA in NCC/PLA composites improves compatibilization between NCC and PLA, and promotes dispersion of NCC in the PLA matrix. More finely dispersed NCC enhances the crystallization nucleation of PLA, resulting in lower crystallization temperature and higher crystallinity. Mechanical properties of NCC/mPLA/PLA composite increase then decrease with increasing mPLA content, when the content of mPLA is 8%, the tensile strength and elastic modulus increase about 30.2% and 41.4% respectively in comparison with those of composite without mPLA. The hydrophilic NCC accelerates degradation of NCC/PLA composite, when mPLA is added, the degradation rate of NCC/PLA composite slowes down but is still higher than that of pure PLA.
2016, 33(12): 2725-2731.
doi: 10.13801/j.cnki.fhclxb.20160315.005
Abstract:
Dodecyl alcohol (DA) was coated with melamine-formaldehyde (MF) and polyethylene glycol modified melamine-formaldehyde (PMF) resin to prepare microencapsulated phase change materials (MicroPCMs). They were respectively added into wood flour/high-density polyethylene (WF/HDPE) composites to obtain MicroPCMs-WF/HDPE composites with thermal energy storage capacity. The surface morphology and mechanical properties of MicroPCMs were characterized by SEM, FTIR and nanoindentor etc. The physical and mechanical and thermal properties of MicroPCMs-WF/HDPE composites were investigated. The results show that the elastic modulus and hardness of modified microcapsules (PMF-MicropCMs) increase by 13.9% and 30.0% compared to unmodified microcapsules (MF-MicroPCMs) after polyethylene glycol modification, respectively. The melting temperature range (22.2-28.7℃) of MicroPCMs-WF/HDPE composites fits the human comfortable temperature range, and the temperature change speed is lower than pure WF/HDPE composites. The incorporation of MicroPCMs has a negative effect on flexural and tensile properties of WF/HDPE composites but favor the moisture absorption performance, impact strength and surface hardness; All properties of PMF-MicroPCMs-WF/HDPE composites are better than those of MF-MicroPCMs-WF/HDPE composites. All the mechanical properties meet the requirements for wood plastic decorative boards.
Dodecyl alcohol (DA) was coated with melamine-formaldehyde (MF) and polyethylene glycol modified melamine-formaldehyde (PMF) resin to prepare microencapsulated phase change materials (MicroPCMs). They were respectively added into wood flour/high-density polyethylene (WF/HDPE) composites to obtain MicroPCMs-WF/HDPE composites with thermal energy storage capacity. The surface morphology and mechanical properties of MicroPCMs were characterized by SEM, FTIR and nanoindentor etc. The physical and mechanical and thermal properties of MicroPCMs-WF/HDPE composites were investigated. The results show that the elastic modulus and hardness of modified microcapsules (PMF-MicropCMs) increase by 13.9% and 30.0% compared to unmodified microcapsules (MF-MicroPCMs) after polyethylene glycol modification, respectively. The melting temperature range (22.2-28.7℃) of MicroPCMs-WF/HDPE composites fits the human comfortable temperature range, and the temperature change speed is lower than pure WF/HDPE composites. The incorporation of MicroPCMs has a negative effect on flexural and tensile properties of WF/HDPE composites but favor the moisture absorption performance, impact strength and surface hardness; All properties of PMF-MicroPCMs-WF/HDPE composites are better than those of MF-MicroPCMs-WF/HDPE composites. All the mechanical properties meet the requirements for wood plastic decorative boards.
2016, 33(12): 2732-2739.
doi: 10.13801/j.cnki.fhclxb.20160315.006
Abstract:
The unidirectional outer of bamboo fibers (OBF)/unsaturated polyester resin (UP) composites were produced with unidirectional continuous OBF and UP. The effects of OBF content on longitudinal static mechanical properties and dynamic mechanical properties of OBF/UP composites were studied. SEM was used to observe tensile cross-section interface combination condition of composites. The results show that the static mechanical properties of OBF/UP composites increase with OBF content up to 50wt% and then decrease. When the OBF content is 50wt%, the properties of composites including tensile properties and flexural properties are most excellent. And the tensile strength, tensile modulus, flexural strength and flexural modulus of the composites are 285.52 MPa, 16.06 GPa, 359.80 MPa and 27.32 GPa, respectively; the storage modulus of OBF/UP composites increase at first, then decreases with the increase of OBF content. When OBF content is 50wt%, the storage modulus of OBF/UP composites yields the highest value. With the increase of OBF content, the glass transition temperature of OBF/UP composites decreases, and the width of the loss peak becomes broader. The cross-section microstructure indicates that the interface bonding strength is better for composites with 50wt% OBF content. The OBF/UP composites have excellent mechanical properties, which have the potential to replace the application of glass fibers reinforced plastic composites in the field of wind power blade materials, highway barrier materials, ship materials and so on.
The unidirectional outer of bamboo fibers (OBF)/unsaturated polyester resin (UP) composites were produced with unidirectional continuous OBF and UP. The effects of OBF content on longitudinal static mechanical properties and dynamic mechanical properties of OBF/UP composites were studied. SEM was used to observe tensile cross-section interface combination condition of composites. The results show that the static mechanical properties of OBF/UP composites increase with OBF content up to 50wt% and then decrease. When the OBF content is 50wt%, the properties of composites including tensile properties and flexural properties are most excellent. And the tensile strength, tensile modulus, flexural strength and flexural modulus of the composites are 285.52 MPa, 16.06 GPa, 359.80 MPa and 27.32 GPa, respectively; the storage modulus of OBF/UP composites increase at first, then decreases with the increase of OBF content. When OBF content is 50wt%, the storage modulus of OBF/UP composites yields the highest value. With the increase of OBF content, the glass transition temperature of OBF/UP composites decreases, and the width of the loss peak becomes broader. The cross-section microstructure indicates that the interface bonding strength is better for composites with 50wt% OBF content. The OBF/UP composites have excellent mechanical properties, which have the potential to replace the application of glass fibers reinforced plastic composites in the field of wind power blade materials, highway barrier materials, ship materials and so on.
2016, 33(12): 2740-2748.
doi: 10.13801/j.cnki.fhclxb.20160317.002
Abstract:
The glass fiber reinforced polypropylene (GF/PP) composite laminates were prepared by hot molding press. Phase transition parameters were obtained by using differential scanning calorimetry (DSC) method. The variation characteristics of temperature field on the moulding processing of GF/PP composites was studied by using ANSYS finite element analysis, which provides a theoretical guidance and basis for optimizing the molding press process. The nonlinear relationship between thermodynamic parameters of composite and the temperature were defined into the material properties. The mechanical performance evaluation index of the material was evaluated by measuring the compression strength, interlaminar shear strength and impact toughness. The effect of preparation process on the mechanical properties of GF/PP composite laminates was discussed and analyzed using response hook surface methodology. The optimized molding press preparation parameters and the mechanical performance of composite laminates were obtained which laid the technology foundation for the automated placement of GF/PP composite. Test results show that the influence degrees of molding press process parameters for the mechanical performance of composite laminates are as follows:heating press temperature, heat holding time and heat holding pressure. The better molding press heating process parameters and the mechanical performance are as follows:heating temperature of 228℃, heating holding time of 6 min, holding pressure of 1.1 MPa and interlaminar shear strength of 31.12 MPa, compression strength of 100.96 MPa, impact toughness of 2.27 kJ/cm2.
The glass fiber reinforced polypropylene (GF/PP) composite laminates were prepared by hot molding press. Phase transition parameters were obtained by using differential scanning calorimetry (DSC) method. The variation characteristics of temperature field on the moulding processing of GF/PP composites was studied by using ANSYS finite element analysis, which provides a theoretical guidance and basis for optimizing the molding press process. The nonlinear relationship between thermodynamic parameters of composite and the temperature were defined into the material properties. The mechanical performance evaluation index of the material was evaluated by measuring the compression strength, interlaminar shear strength and impact toughness. The effect of preparation process on the mechanical properties of GF/PP composite laminates was discussed and analyzed using response hook surface methodology. The optimized molding press preparation parameters and the mechanical performance of composite laminates were obtained which laid the technology foundation for the automated placement of GF/PP composite. Test results show that the influence degrees of molding press process parameters for the mechanical performance of composite laminates are as follows:heating press temperature, heat holding time and heat holding pressure. The better molding press heating process parameters and the mechanical performance are as follows:heating temperature of 228℃, heating holding time of 6 min, holding pressure of 1.1 MPa and interlaminar shear strength of 31.12 MPa, compression strength of 100.96 MPa, impact toughness of 2.27 kJ/cm2.
2016, 33(12): 2749-2756.
doi: 10.13801/j.cnki.fhclxb.20160324.004
Abstract:
In order to optimize the liquid forming process of the complex perform structure, the resin flow during composite liquid molding process was simulated base on the finite element method/life and death node method. The molding process of the typical rectangle plate, circle plate structure and I rib reinforced panel was simulated and verified. The results show that the simulation results of molding process for typical rectangle plate and circle plate structure are in good agreement with the theoretical solutions, which verify the validation of the life and death node method in the resin flow front tracking. The molding process simulation of the non-uniform thickness cylinder with cavity and the cube three-dimensional entity structure verify the applicability of finite element method for the three-dimensional structure. The simulation method of liquid molding process base on the finite element method/life and death node method is more adaptive to the complex solution region, which can be used to predict the resin flow law of liquid molding process for the complex entity structure, guide the design and process optimization of the mould.
In order to optimize the liquid forming process of the complex perform structure, the resin flow during composite liquid molding process was simulated base on the finite element method/life and death node method. The molding process of the typical rectangle plate, circle plate structure and I rib reinforced panel was simulated and verified. The results show that the simulation results of molding process for typical rectangle plate and circle plate structure are in good agreement with the theoretical solutions, which verify the validation of the life and death node method in the resin flow front tracking. The molding process simulation of the non-uniform thickness cylinder with cavity and the cube three-dimensional entity structure verify the applicability of finite element method for the three-dimensional structure. The simulation method of liquid molding process base on the finite element method/life and death node method is more adaptive to the complex solution region, which can be used to predict the resin flow law of liquid molding process for the complex entity structure, guide the design and process optimization of the mould.
2016, 33(12): 2757-2765.
doi: 10.13801/j.cnki.fhclxb.20160328.007
Abstract:
In order to investigate the drilling bitgeometry of carbon fiber reinforced composite (CFRP) laminates which achieves low defect, T800 CFRP laminates were studied by drilling experiments adopting four kinds of different geometry for drill bits. The effect of drill bit geometry on thrust force of drilling was analyzed. The relationship between thrust force of drilling and delamination damage was discussed. The results show that dropping speed of thrust force and outlet delamination factor have a good positive correlation. Dropping speed of thrust force can characterize the applicability of drill bit geometry to CFRP laminates drilling. In addition, the experiments show that cutting areas of drill bits which have multi-step geometric characters would cause thrust force returning to zero slowly in multi stages during drilling through the exit of the workpiece, and generating lower delamination factor at exit.
In order to investigate the drilling bitgeometry of carbon fiber reinforced composite (CFRP) laminates which achieves low defect, T800 CFRP laminates were studied by drilling experiments adopting four kinds of different geometry for drill bits. The effect of drill bit geometry on thrust force of drilling was analyzed. The relationship between thrust force of drilling and delamination damage was discussed. The results show that dropping speed of thrust force and outlet delamination factor have a good positive correlation. Dropping speed of thrust force can characterize the applicability of drill bit geometry to CFRP laminates drilling. In addition, the experiments show that cutting areas of drill bits which have multi-step geometric characters would cause thrust force returning to zero slowly in multi stages during drilling through the exit of the workpiece, and generating lower delamination factor at exit.
2016, 33(12): 2766-2774.
doi: 10.13801/j.cnki.fhclxb.20160328.001
Abstract:
A three-dimensional damage numerical model was proposed based on continuum damage mechanics (CDM) to deal with problem of the notched strength of composite laminates. This model was able to distinguish different failure modes of in-plane damage (fiber failure, inter fiber failure) and interlaminar delamination damage. Three-dimensional Puck criterion and Aymerich criterion were used to judge two kinds of damage above. The damage was evolved based on the linear softening model of CDM after material failure. The in-situ effect and the shear nonlinear behavior of composite laminate sublayers were considered in the model. The tensile strength of notched AS4/3501-6 laminate tested by Carlsson was numerical simulated. The results show that the analysis results are in good agreement with the test results. The analysis results prove that the present model is capable of predicting the in-plane tensile strength of notched composite laminates.
A three-dimensional damage numerical model was proposed based on continuum damage mechanics (CDM) to deal with problem of the notched strength of composite laminates. This model was able to distinguish different failure modes of in-plane damage (fiber failure, inter fiber failure) and interlaminar delamination damage. Three-dimensional Puck criterion and Aymerich criterion were used to judge two kinds of damage above. The damage was evolved based on the linear softening model of CDM after material failure. The in-situ effect and the shear nonlinear behavior of composite laminate sublayers were considered in the model. The tensile strength of notched AS4/3501-6 laminate tested by Carlsson was numerical simulated. The results show that the analysis results are in good agreement with the test results. The analysis results prove that the present model is capable of predicting the in-plane tensile strength of notched composite laminates.
2016, 33(12): 2775-2780.
doi: 10.13801/j.cnki.fhclxb.20160323.001
Abstract:
We analyzed the material resistivity. Carbon fiber volume fraction is the main factor influencing the material resistivity. According to the measured data of material surface, carbon fiber volume fraction of material can be estimated. According to the measured data of multiple specimens, the relationship curve between carbon fiber volume fraction and resistivity of material can be fitted. So according to the estimated data of the carbon fiber volume fraction, the resistivity of the material can be estimated. According to the braiding angle and pitch length of 3D braided carbon fiber composites, the resistivity of material can be estimated, which can be used for material analysis of eddy current nondestructive testing.
We analyzed the material resistivity. Carbon fiber volume fraction is the main factor influencing the material resistivity. According to the measured data of material surface, carbon fiber volume fraction of material can be estimated. According to the measured data of multiple specimens, the relationship curve between carbon fiber volume fraction and resistivity of material can be fitted. So according to the estimated data of the carbon fiber volume fraction, the resistivity of the material can be estimated. According to the braiding angle and pitch length of 3D braided carbon fiber composites, the resistivity of material can be estimated, which can be used for material analysis of eddy current nondestructive testing.
2016, 33(12): 2781-2788.
doi: 10.13801/j.cnki.fhclxb.20160324.003
Abstract:
Combined temperature and humid environment experiment with damping property measurement technology, the experiment platform to test the damping properties of the embedded co-cured composite in heat and humidity environment was established. The new method using the least-square method was presented to analyze the relative damping coefficient. The effect curves of temperature, humidity and heat coupling parameters on damping coefficient of the embedded co-cured carbon fiber/bismaleimide composites were investigated respectively. The results show that the relative damping coefficient of the embedded co-cured composites is firstly enhancing and then decreasing lastly increasing with temperature increase. Under the effect of humidity and heat coupling environment, relative damping coefficient increases with humidity and temperature increase. The conclusion will lay a foundation for the design and application under all-weather environment of the new composite damping structure.
Combined temperature and humid environment experiment with damping property measurement technology, the experiment platform to test the damping properties of the embedded co-cured composite in heat and humidity environment was established. The new method using the least-square method was presented to analyze the relative damping coefficient. The effect curves of temperature, humidity and heat coupling parameters on damping coefficient of the embedded co-cured carbon fiber/bismaleimide composites were investigated respectively. The results show that the relative damping coefficient of the embedded co-cured composites is firstly enhancing and then decreasing lastly increasing with temperature increase. Under the effect of humidity and heat coupling environment, relative damping coefficient increases with humidity and temperature increase. The conclusion will lay a foundation for the design and application under all-weather environment of the new composite damping structure.
2016, 33(12): 2789-2796.
doi: 10.13801/j.cnki.fhclxb.20160323.002
Abstract:
For ultra-high property and ultra-high molecular weight polyethylene fiber's (UHMWPE) characteristics, three kinds of knitted fabric including weft plain, rib, cardigan were successfully woven. The six-layers rib weft plain, six-layers and six-layers cardigan knitted composites were made by vacuum assisted resin transfer molding (VARTM) technology. Compression tests of three kinds of composites were conducted. And then we analyzed the specific compressive strength-strain curves, specific compression energy-strain curves, specific compression energy-strain fitting curves, and discussed the energy absorbing condition and damage form during the compression process and. The results show that the specific compression strength and specific compression energy of weft plain knitted composites are the biggest, the second is rib, the cardigan is minimum. And three weft knitted structural composites' compression fracture is not brittle fracture. Because of the good flexibility of the composites, samples' specific compression energy and compressive strain show linear correlation. For the composites of same structure, the longitudinal and transverse specific compression strength-strain curves, specific compression energy-strain curves are nearly coincident. The damage along reinforced structural matrix and deformation of resin plastic are the main forms of damage to the material.
For ultra-high property and ultra-high molecular weight polyethylene fiber's (UHMWPE) characteristics, three kinds of knitted fabric including weft plain, rib, cardigan were successfully woven. The six-layers rib weft plain, six-layers and six-layers cardigan knitted composites were made by vacuum assisted resin transfer molding (VARTM) technology. Compression tests of three kinds of composites were conducted. And then we analyzed the specific compressive strength-strain curves, specific compression energy-strain curves, specific compression energy-strain fitting curves, and discussed the energy absorbing condition and damage form during the compression process and. The results show that the specific compression strength and specific compression energy of weft plain knitted composites are the biggest, the second is rib, the cardigan is minimum. And three weft knitted structural composites' compression fracture is not brittle fracture. Because of the good flexibility of the composites, samples' specific compression energy and compressive strain show linear correlation. For the composites of same structure, the longitudinal and transverse specific compression strength-strain curves, specific compression energy-strain curves are nearly coincident. The damage along reinforced structural matrix and deformation of resin plastic are the main forms of damage to the material.
2016, 33(12): 2797-2806.
doi: 10.13801/j.cnki.fhclxb.20160224.001
Abstract:
M40 graphite fiber was selected as reinforced material, continuous M40/Al composites whose volume fraction of fiber was 40% and matrix alloys were ZL102, ZL114A, ZL205A and ZL301 alloys respectively were prepared by vacuum gas pressure infiltration, and M40 fibers were extracted using NaOH solution, thus the effects of matrix alloy on the fiber damage and fracture mechanism of continuous M40/Al composites were investigated. The results show that the damages caused by different matrix alloys to M40 fibers are quite different, the tensile strength of fiber extracted from M40/ZL301 composite is the highest, the tensile strength of it is 1 686 MPa, which is about 38.3% of the raw silk tensile strength. While the tensile strength of fiber extracted from M40/ZL102 composite is the lowest, the tensile strength is only 687 MPa, and the roughness of fiber surface is different. There are obvious differences for the fracture mechanisms of different M40/Al composites, when M40/ZL102 and M40/ZL114A composites fracture, there are no fiber pulling out and interfacial debonding, crack passes through fiber transversely, which leads to the failure of composites at low stress. While M40/ZL205A composite shows a small amount of fiber pulling out and slight interfacial debonding. At the same time, M40/ZL301 composite shows a large number of fiber pulling out, crack extends along the interface longitudinally, the interface debonding is obvious, fiber gives full play to its bearing function, and the tensile strength of composite is the highest, which reaches 670.2 MPa.
M40 graphite fiber was selected as reinforced material, continuous M40/Al composites whose volume fraction of fiber was 40% and matrix alloys were ZL102, ZL114A, ZL205A and ZL301 alloys respectively were prepared by vacuum gas pressure infiltration, and M40 fibers were extracted using NaOH solution, thus the effects of matrix alloy on the fiber damage and fracture mechanism of continuous M40/Al composites were investigated. The results show that the damages caused by different matrix alloys to M40 fibers are quite different, the tensile strength of fiber extracted from M40/ZL301 composite is the highest, the tensile strength of it is 1 686 MPa, which is about 38.3% of the raw silk tensile strength. While the tensile strength of fiber extracted from M40/ZL102 composite is the lowest, the tensile strength is only 687 MPa, and the roughness of fiber surface is different. There are obvious differences for the fracture mechanisms of different M40/Al composites, when M40/ZL102 and M40/ZL114A composites fracture, there are no fiber pulling out and interfacial debonding, crack passes through fiber transversely, which leads to the failure of composites at low stress. While M40/ZL205A composite shows a small amount of fiber pulling out and slight interfacial debonding. At the same time, M40/ZL301 composite shows a large number of fiber pulling out, crack extends along the interface longitudinally, the interface debonding is obvious, fiber gives full play to its bearing function, and the tensile strength of composite is the highest, which reaches 670.2 MPa.
2016, 33(12): 2807-2814.
doi: 10.13801/j.cnki.fhclxb.20160317.006
Abstract:
In order to solve the problem that the hydrodynamic oil film formed during the work process of sintering materials is easy to seepage into porous medium which leads to the degradation of lubrication property, multi-layer sintered materials with different porosity structures were prepared by powder metallurgical technique to achieve the unification of high load capacity and good lubricating property. Fluid lubrication model of the multi-layer sintered materials in polar coordinates was established based on Darcy's law firstly, numerical simulation were conducted by using the finite difference method, and the effects of surface Darcy flow on the lubrication property of oil film under different rotate speeds were investigated. Then, the end face friction experiment were conducted under oil lubrication to verify the simulation results. The results show that the oil film lubrication property of the multi-layer sintered materials is much more better than that of the ordinary monolayer sintered materials. With the decrease of the surface porosity, the lubrication property of the multi-layer sintered materials becomes better in the given range of the porosity. The oil film lubrication property of multi-layer sintered materials is improved relatively when considering the surface Darcy flow, and the improving effect becoming obvious gradually with the rotate speed increases. There is a good agreement between the conclusions obtained by friction test and numerical analysis. The research work can provide theoretical bases for tribological property analysis and structure design of the multi-layer sintered material at some degree.
In order to solve the problem that the hydrodynamic oil film formed during the work process of sintering materials is easy to seepage into porous medium which leads to the degradation of lubrication property, multi-layer sintered materials with different porosity structures were prepared by powder metallurgical technique to achieve the unification of high load capacity and good lubricating property. Fluid lubrication model of the multi-layer sintered materials in polar coordinates was established based on Darcy's law firstly, numerical simulation were conducted by using the finite difference method, and the effects of surface Darcy flow on the lubrication property of oil film under different rotate speeds were investigated. Then, the end face friction experiment were conducted under oil lubrication to verify the simulation results. The results show that the oil film lubrication property of the multi-layer sintered materials is much more better than that of the ordinary monolayer sintered materials. With the decrease of the surface porosity, the lubrication property of the multi-layer sintered materials becomes better in the given range of the porosity. The oil film lubrication property of multi-layer sintered materials is improved relatively when considering the surface Darcy flow, and the improving effect becoming obvious gradually with the rotate speed increases. There is a good agreement between the conclusions obtained by friction test and numerical analysis. The research work can provide theoretical bases for tribological property analysis and structure design of the multi-layer sintered material at some degree.
2016, 33(12): 2815-2823.
doi: 10.13801/j.cnki.fhclxb.20160129.003
Abstract:
In order to meet the urgent needs of low-voltage electrical equipment for high quality electrical contact materials, and to protect the scarce resources and reduce the cost of electrical contact at the same time, doped nano-SnO2-Al2O3/Cu novel electrical contact composites were fabricated by using powder metallurgy technique. The electrical conductivity, hardness and wear resistances of them were also investigated. The results show that both of re-sintering and cold deformation processes can improve the sintering quality, density, electrical conductivity as well as hardness of the composites significantly. With the increasing for total content of nano-Al2O3 and doped nano-SnO2 particles, hardness and wear resistances of the doped nano-SnO2-Al2O3/Cu electrical contact composites show the same change rule, which increases firstly and then decreases. When the total content of nano-Al2O3 and doped nano-SnO2 particles is 0.80wt%, both of the hardness and wear resistances of the composites reach the optimum. While when the total content of nano-Al2O3 and doped nano-SnO2 particles remains unchanged at 0.80wt%, with the content of nano-Al2O3 particles increasing, the hardness and wear resistances of the doped nano-SnO2-Al2O3/Cu electrical contact composites enhance. When the content of doped nano-SnO2 particles is 0, the wear resistance of the composite reaches the optimum. Therefore, compared with doped nano-SnO2 particles, the nano-Al2O3 particles have a more significant improving effect on the wear resistance of the doped nano-SnO2-Al2O3/Cu electrical contact composites.
In order to meet the urgent needs of low-voltage electrical equipment for high quality electrical contact materials, and to protect the scarce resources and reduce the cost of electrical contact at the same time, doped nano-SnO2-Al2O3/Cu novel electrical contact composites were fabricated by using powder metallurgy technique. The electrical conductivity, hardness and wear resistances of them were also investigated. The results show that both of re-sintering and cold deformation processes can improve the sintering quality, density, electrical conductivity as well as hardness of the composites significantly. With the increasing for total content of nano-Al2O3 and doped nano-SnO2 particles, hardness and wear resistances of the doped nano-SnO2-Al2O3/Cu electrical contact composites show the same change rule, which increases firstly and then decreases. When the total content of nano-Al2O3 and doped nano-SnO2 particles is 0.80wt%, both of the hardness and wear resistances of the composites reach the optimum. While when the total content of nano-Al2O3 and doped nano-SnO2 particles remains unchanged at 0.80wt%, with the content of nano-Al2O3 particles increasing, the hardness and wear resistances of the doped nano-SnO2-Al2O3/Cu electrical contact composites enhance. When the content of doped nano-SnO2 particles is 0, the wear resistance of the composite reaches the optimum. Therefore, compared with doped nano-SnO2 particles, the nano-Al2O3 particles have a more significant improving effect on the wear resistance of the doped nano-SnO2-Al2O3/Cu electrical contact composites.
2016, 33(12): 2824-2830.
doi: 10.13801/j.cnki.fhclxb.20160322.007
Abstract:
To prepare a uniformly dispersed short carbon fibre (Cf)/Cu composite in Cu matrix which contained a large volume fraction of Cf, by an electro-chemical method in the process of Cu plating on the surface of Cf, a parallel Cu fosil was used as cathode instead of long carbon fibre bundle.By which, more homogeneous and smooth Cu-plating short Cf were obtained. Based on that, the 46vol% Cf/Cu composite (sample 1)was prepared directly by spark plasma sintering (SPS) with those Cf/Cu composite filament prepared at 2 V, 30 min. Then non-coated Cf mixed with Cu powder were used to prepare another Cf/Cu composite(sample 2).The phase composition, surface and fracture morphology of Cf/Cu composite filament and the Cf/Cu composites were researched through XRD and SEM. After that, there was a comparison with these samples on the mechanical properties.Results show that the Cu coating creates discontinuous fractures under load, which causes fluctuations in the tensile load-displacement curve of Cf/Cu composite filament. Besides, the uniformity and mechanical properties of sample 1 are higher than sample 2. The tensile strengths of Cf/Cu composites made by two different ways are lower than Cu, but the yield strengths are higher.
To prepare a uniformly dispersed short carbon fibre (Cf)/Cu composite in Cu matrix which contained a large volume fraction of Cf, by an electro-chemical method in the process of Cu plating on the surface of Cf, a parallel Cu fosil was used as cathode instead of long carbon fibre bundle.By which, more homogeneous and smooth Cu-plating short Cf were obtained. Based on that, the 46vol% Cf/Cu composite (sample 1)was prepared directly by spark plasma sintering (SPS) with those Cf/Cu composite filament prepared at 2 V, 30 min. Then non-coated Cf mixed with Cu powder were used to prepare another Cf/Cu composite(sample 2).The phase composition, surface and fracture morphology of Cf/Cu composite filament and the Cf/Cu composites were researched through XRD and SEM. After that, there was a comparison with these samples on the mechanical properties.Results show that the Cu coating creates discontinuous fractures under load, which causes fluctuations in the tensile load-displacement curve of Cf/Cu composite filament. Besides, the uniformity and mechanical properties of sample 1 are higher than sample 2. The tensile strengths of Cf/Cu composites made by two different ways are lower than Cu, but the yield strengths are higher.
2016, 33(12): 2831-2839.
doi: 10.13801/j.cnki.fhclxb.20160125.002
Abstract:
In order to fabricate a novel formaldehyde removal material with high proformance, reduced graphene oxide (RGO)/MnO2 aerogel was fabricated by hydrothermal method. The morphological structures and properties of RGO/MnO2 aerogel were characterized by SEM, TEM, TGA, XPS and BET, and the removal activities of RGO/MnO2 aerogel for formaldehyde were investigated. The results show that among the precursors of RGO/MnO2 aerogel, graphene oxide (GO) is proved to be single-layer two-dimensional nanosheets, MnO2 aerogel consists of MnO2 nanowires, the diameter of MnO2 nanowires is about 40 nm, the length reaches above 5 μm, and belongs to cryptomelane structure. RGO/MnO2 aerogel is a material which have three-dimensional porous structure consists of flake materials, and such flake materials are made of homogeneously dispersed RGO nanosheets and MnO2 nanowires, RGO nanosheets act as clapboards which separate MnO2 nanowires and makes MnO2 nanowires homogeneously dispersed in RGO. RGO/MnO2 aerogel has favorable thermal stability under 100℃. RGO/MnO2 aerogel possesses a preferable removal activity for formaldehyde with low concentration, the removal ratio is 62.5%, the removal rate for formaldehyde of RGO/MnO2 aerogel under the same condition is improved by 30.0% comparing with that of MnO2 aerogel, which proves that RGO is beneficial for enhancing the removal activity of MnO2 for formaldehyde.
In order to fabricate a novel formaldehyde removal material with high proformance, reduced graphene oxide (RGO)/MnO2 aerogel was fabricated by hydrothermal method. The morphological structures and properties of RGO/MnO2 aerogel were characterized by SEM, TEM, TGA, XPS and BET, and the removal activities of RGO/MnO2 aerogel for formaldehyde were investigated. The results show that among the precursors of RGO/MnO2 aerogel, graphene oxide (GO) is proved to be single-layer two-dimensional nanosheets, MnO2 aerogel consists of MnO2 nanowires, the diameter of MnO2 nanowires is about 40 nm, the length reaches above 5 μm, and belongs to cryptomelane structure. RGO/MnO2 aerogel is a material which have three-dimensional porous structure consists of flake materials, and such flake materials are made of homogeneously dispersed RGO nanosheets and MnO2 nanowires, RGO nanosheets act as clapboards which separate MnO2 nanowires and makes MnO2 nanowires homogeneously dispersed in RGO. RGO/MnO2 aerogel has favorable thermal stability under 100℃. RGO/MnO2 aerogel possesses a preferable removal activity for formaldehyde with low concentration, the removal ratio is 62.5%, the removal rate for formaldehyde of RGO/MnO2 aerogel under the same condition is improved by 30.0% comparing with that of MnO2 aerogel, which proves that RGO is beneficial for enhancing the removal activity of MnO2 for formaldehyde.
2016, 33(12): 2840-2845.
doi: 10.13801/j.cnki.fhclxb.20160322.001
Abstract:
Relationship of densities between Cf/SiC composites and C/C preforms was studied by theoretical calculation. And 2D Cf/SiC composites were prepared from three kinds of C/C preforms with densities of 0.98, 1.06, 1.12 g/cm3, which were prepared by repeatedly overlapping the layers of carbon cloths and precursor infiltration pyrolysis, by liquid silicon infiltration. The effects of densities of C/C preforms on structure and property of composites were study. The results were compared with theoretical calculation results. The research results show that the test results are basically consistent with the theoretical mathematical results. The density of Cf/SiC composites increases first and then decreases with the increase of the C/C preforms density. And when the density of C/C preform is greater than 0.98 g/cm3, the flexural strength of composites decreases with the increase of C/C preforms density. The composites have a better structure and property, while the density of C/C preforms is 0.98 g/cm3.
Relationship of densities between Cf/SiC composites and C/C preforms was studied by theoretical calculation. And 2D Cf/SiC composites were prepared from three kinds of C/C preforms with densities of 0.98, 1.06, 1.12 g/cm3, which were prepared by repeatedly overlapping the layers of carbon cloths and precursor infiltration pyrolysis, by liquid silicon infiltration. The effects of densities of C/C preforms on structure and property of composites were study. The results were compared with theoretical calculation results. The research results show that the test results are basically consistent with the theoretical mathematical results. The density of Cf/SiC composites increases first and then decreases with the increase of the C/C preforms density. And when the density of C/C preform is greater than 0.98 g/cm3, the flexural strength of composites decreases with the increase of C/C preforms density. The composites have a better structure and property, while the density of C/C preforms is 0.98 g/cm3.
2016, 33(12): 2846-2853.
doi: 10.13801/j.cnki.fhclxb.20160330.002
Abstract:
The tensile mechanical properties of two dimensional C/SiC composites at 4 strain rates (0.001, 0.010, 90.000 and 350.000 s-1) were investigated by split Hopkinson tensile bar device and an electronic universal test machine. The stress equilibrium status in the dynamic experiment was calculated and verified. SEM was employed to analyze the damage fracture and failure mechanism of the composites at different strain rates. The damage and strain rate related constitutive equation of the composites was established. The results show that the stress-strain curves of the two dimensional C/SiC composites show non-linearity characteristics. The tensile strength increases from 204 MPa to 270 MPa, up by 33% with the increase of strain rate for two dimensional C/SiC composites, testifying the strong strain rate sensitivity of the tensile strength for the composites. The composites show different failure modes under quasi-static and dynamic loading, which are caused by the strain rate effect on the interface behavior in the material.
The tensile mechanical properties of two dimensional C/SiC composites at 4 strain rates (0.001, 0.010, 90.000 and 350.000 s-1) were investigated by split Hopkinson tensile bar device and an electronic universal test machine. The stress equilibrium status in the dynamic experiment was calculated and verified. SEM was employed to analyze the damage fracture and failure mechanism of the composites at different strain rates. The damage and strain rate related constitutive equation of the composites was established. The results show that the stress-strain curves of the two dimensional C/SiC composites show non-linearity characteristics. The tensile strength increases from 204 MPa to 270 MPa, up by 33% with the increase of strain rate for two dimensional C/SiC composites, testifying the strong strain rate sensitivity of the tensile strength for the composites. The composites show different failure modes under quasi-static and dynamic loading, which are caused by the strain rate effect on the interface behavior in the material.
2016, 33(12): 2854-2859.
doi: 10.13801/j.cnki.fhclxb.20160224.002
Abstract:
Laminated SiC whisker (SiCW)/SiC ceramic composites were fabricated by tape casting and chemical vapor infiltration (TC-CVI) process and the effect of SiCW content on the mechanical properties and microstructures of laminated ceramic composites was discussed. Strengthening/toughening mechanisms of laminated SiCW/SiC ceramic composites were investigated. The results indicate that TC-CVI process can effectively increase the content of whiskers (40vol%) in composites and reduce the damage to whiskers during fabrication process. Moreover, the fabricated laminated SiCW/SiC ceramic composites have appropriate interface bonding strength of interfacial and interlaminar. When SiCW content increases, both of the density and mechanical properties of the laminated ceramic composites can be significantly improved. The density, flexural strength and fracture toughness of laminated SiCW/SiC ceramic composites with 40vol% whisker are respectively 8.4%, 30.8% and 26.7% higher than those of laminated SiCW/SiC ceramic composites with 25vol% whisker. Interfacial and interlaminar crack deflection, and interfacial crack bridging and whisker pull-out can be observed in the fracture morphologies, which are main toughening mechanisms. Large content of SiCW and appropriate interface bonding strength between interfacial and interlaminar can obviously improve the strength and toughness of laminated SiCW/SiC ceramic composites together.
Laminated SiC whisker (SiCW)/SiC ceramic composites were fabricated by tape casting and chemical vapor infiltration (TC-CVI) process and the effect of SiCW content on the mechanical properties and microstructures of laminated ceramic composites was discussed. Strengthening/toughening mechanisms of laminated SiCW/SiC ceramic composites were investigated. The results indicate that TC-CVI process can effectively increase the content of whiskers (40vol%) in composites and reduce the damage to whiskers during fabrication process. Moreover, the fabricated laminated SiCW/SiC ceramic composites have appropriate interface bonding strength of interfacial and interlaminar. When SiCW content increases, both of the density and mechanical properties of the laminated ceramic composites can be significantly improved. The density, flexural strength and fracture toughness of laminated SiCW/SiC ceramic composites with 40vol% whisker are respectively 8.4%, 30.8% and 26.7% higher than those of laminated SiCW/SiC ceramic composites with 25vol% whisker. Interfacial and interlaminar crack deflection, and interfacial crack bridging and whisker pull-out can be observed in the fracture morphologies, which are main toughening mechanisms. Large content of SiCW and appropriate interface bonding strength between interfacial and interlaminar can obviously improve the strength and toughness of laminated SiCW/SiC ceramic composites together.
2016, 33(12): 2860-2868.
doi: 10.13801/j.cnki.fhclxb.20160328.010
Abstract:
Generalized differential quadrature (GDQ) method was used to analyze and optimize the vibration and buckling of composite laminate under different boundary conditions and linearly varying in-plane loads. Since GDQ method led to calculation oscillation and non-convergence for the case of buckling for composite laminate under linearly varying in-plane loads, load perturbation strategy was developed to achieve the stable and efficient computation of buckling for composite laminate by GDQ method. Influence of ply angle on the comprehensive performance of composite laminate was analyzed base on the normalized index of fundamental circle frequency and critical buckling load coefficient, while the stacking sequence of composite laminate was optimized by using the direction search simulated annealing algorithm. The results show that ply angle variation has greater effect on buckling performance than frequency. Boundary condition is the least one to affect the optimal comprehensive performance of composite laminate under the bending load in the family of linearly varying in-plane loads, on the contrary, the most dominant factor to affect the optimal ply angle. The study provides a reference for the design of composite laminate under complex loading.
Generalized differential quadrature (GDQ) method was used to analyze and optimize the vibration and buckling of composite laminate under different boundary conditions and linearly varying in-plane loads. Since GDQ method led to calculation oscillation and non-convergence for the case of buckling for composite laminate under linearly varying in-plane loads, load perturbation strategy was developed to achieve the stable and efficient computation of buckling for composite laminate by GDQ method. Influence of ply angle on the comprehensive performance of composite laminate was analyzed base on the normalized index of fundamental circle frequency and critical buckling load coefficient, while the stacking sequence of composite laminate was optimized by using the direction search simulated annealing algorithm. The results show that ply angle variation has greater effect on buckling performance than frequency. Boundary condition is the least one to affect the optimal comprehensive performance of composite laminate under the bending load in the family of linearly varying in-plane loads, on the contrary, the most dominant factor to affect the optimal ply angle. The study provides a reference for the design of composite laminate under complex loading.
2016, 33(12): 2869-2876.
doi: 10.13801/j.cnki.fhclxb.20160219.002
Abstract:
H-PA-LA/SiO2 ternary phase change system composites were prepared with hexadecanol (H)-palmitic acid (PA)-lauric acid (LA) as a phase change material, SiO2 as the carrie material by sol-gel method by different amounts of H-PA-LA. The moisture performance and heat performance of H-PA-LA/SiO2 ternary phase change system composites were tested by isothermal sorption moisture method and cooling curve method, meanwhile composition structure, crystal structure, microstructure, size distribution, phase transition temperature and phase transition enthalpy of H-PA-LA/SiO2 ternary phase change system composites were characterized by FTIR, XRD, SEM, LPSA and DSC. The results show that while H-PA-LA content is 0.06 mol, prepared H-PA-LA/SiO2 ternary phase change system composites have the best heat-moisture comprehensive performance in the range of human comfort, such as equilibrium moisture content is 0.07-0.10 g/g, phase change temperature is 26.29℃, phase change enthalpy is 70.55 J/g in relative humidity 40%-65%.
H-PA-LA/SiO2 ternary phase change system composites were prepared with hexadecanol (H)-palmitic acid (PA)-lauric acid (LA) as a phase change material, SiO2 as the carrie material by sol-gel method by different amounts of H-PA-LA. The moisture performance and heat performance of H-PA-LA/SiO2 ternary phase change system composites were tested by isothermal sorption moisture method and cooling curve method, meanwhile composition structure, crystal structure, microstructure, size distribution, phase transition temperature and phase transition enthalpy of H-PA-LA/SiO2 ternary phase change system composites were characterized by FTIR, XRD, SEM, LPSA and DSC. The results show that while H-PA-LA content is 0.06 mol, prepared H-PA-LA/SiO2 ternary phase change system composites have the best heat-moisture comprehensive performance in the range of human comfort, such as equilibrium moisture content is 0.07-0.10 g/g, phase change temperature is 26.29℃, phase change enthalpy is 70.55 J/g in relative humidity 40%-65%.
2016, 33(12): 2877-2883.
doi: 10.13801/j.cnki.fhclxb.20160126.003
Abstract:
In order to obtain hot structure composites with high performances, a series of two-dimensional carbon/carbon composites was prepared with the domestic T300 carbon fiber as raw material by carbon cloth prepreg layer alternating ply hot pressing and liquid impregnation pyrolysis method, and the microstructure features, mechanical properties and ablation properties of two dimensional carbon/carbon composites were characterized and discussed. The investigation results show that the types of carbon cloth and preparation process have obvious effects on the mechanical properties of two dimensional carbon/carbon composites. When the type of carbon cloth selects eight heddle satin, after carbonization pre-treatment and the temperature of high temperature treatment reaches 2 300℃, the highest values of tensile strength and interlaminar shear strength for two dimensional carbon/carbon composites reach 301 MPa and 12.4 MPa respectively, which reach the international advanced level. The ablation properties for different two dimensional carbon/carbon composites are almost the same under the simulated inspection status of typical service condition. None of them has the ablation peeling off phenomenon due to the low interlaminar strength, showing good ablation uniformity and structural reliability.
In order to obtain hot structure composites with high performances, a series of two-dimensional carbon/carbon composites was prepared with the domestic T300 carbon fiber as raw material by carbon cloth prepreg layer alternating ply hot pressing and liquid impregnation pyrolysis method, and the microstructure features, mechanical properties and ablation properties of two dimensional carbon/carbon composites were characterized and discussed. The investigation results show that the types of carbon cloth and preparation process have obvious effects on the mechanical properties of two dimensional carbon/carbon composites. When the type of carbon cloth selects eight heddle satin, after carbonization pre-treatment and the temperature of high temperature treatment reaches 2 300℃, the highest values of tensile strength and interlaminar shear strength for two dimensional carbon/carbon composites reach 301 MPa and 12.4 MPa respectively, which reach the international advanced level. The ablation properties for different two dimensional carbon/carbon composites are almost the same under the simulated inspection status of typical service condition. None of them has the ablation peeling off phenomenon due to the low interlaminar strength, showing good ablation uniformity and structural reliability.
2016, 33(12): 2884-2892.
doi: 10.13801/j.cnki.fhclxb.20160324.002
Abstract:
As the development of 3D print technology makes the manufacturing of complex graded structures more easily, it is necessary to carrying out the investigations with respect to the solving for complex graded problems. Now, the investigations about the problems that the modulus of beam structures varying along the axial direction or thickness direction grade are already more, while the investigations about the modulus varying along two directions synchronously are less. Thus a graded composite plane beam with modulus changed in exponential form synchronously along thickness direction and axial direction was investigated by using Fourier decomposition in complex form. The general solutions for four-order differential governing equation with variable coefficients were solved firstly by using semi-inverse method of elasticity. Then, the particular solution of the beam subjected to symmetric load effects was derived by series expansions. Finally, the correctness of series solutions was verified by comparing with finite element results. The results show that when the gradient varying in bi-directions, the stress distribution and deformation situations of the beam structure become more complex, that the stress is larger at the region with higher modulus, while the stress is smaller at the region with lower modulus. The series solutions proposed could be also extended to the investigation of other relevant plane or semi-plane inhomogeneous problem with graded varying in bi-directions.
As the development of 3D print technology makes the manufacturing of complex graded structures more easily, it is necessary to carrying out the investigations with respect to the solving for complex graded problems. Now, the investigations about the problems that the modulus of beam structures varying along the axial direction or thickness direction grade are already more, while the investigations about the modulus varying along two directions synchronously are less. Thus a graded composite plane beam with modulus changed in exponential form synchronously along thickness direction and axial direction was investigated by using Fourier decomposition in complex form. The general solutions for four-order differential governing equation with variable coefficients were solved firstly by using semi-inverse method of elasticity. Then, the particular solution of the beam subjected to symmetric load effects was derived by series expansions. Finally, the correctness of series solutions was verified by comparing with finite element results. The results show that when the gradient varying in bi-directions, the stress distribution and deformation situations of the beam structure become more complex, that the stress is larger at the region with higher modulus, while the stress is smaller at the region with lower modulus. The series solutions proposed could be also extended to the investigation of other relevant plane or semi-plane inhomogeneous problem with graded varying in bi-directions.
2016, 33(12): 2893-2904.
doi: 10.13801/j.cnki.fhclxb.20160229.002
Abstract:
Based on employing the TiCl4, cetyltrimethyl ammonium bromide, chloroplatinic acid and conductive carbon felt as titanium source, template agent, doping-ion and carrier, respectively, the precursor solution of liquid crystal-Pt ion-inorganic titanium was prepared by hydrothermal synthesis method. The photoelectrode of Pt doped mesoporous TiO2/conductive carbon felt (TiO2-Pt/CCF) was obtained by the dip-coating method with the aid of ultrasonic system under nitrogen protection. The obtained TiO2-Pt/CCF was characterized by modern analytical tools. The photoelectrocatalytic performance of material was analyzed by degradation of benzaldehyde, and the photoelectrocatalytic synergistic mechanism was analyzed. The results show that the mesoporous processing can increase the specific surface area of TiO2-Pt/CCF, enlarge the degradation reaction area, and increase the concentration of catalyst surface degradation product; the metal ion doping can bring impurity level, reduce the band gap of TiO2, at the same time, Pt acts as a photo-electron and hole trap, and inhibits the electron and hole recombine, improves the photoelectrocatalytic activity of TiO2-Pt/CCF; the TiO2 loading can enhance the absorption and the surface electron transfer of target degradation product. Under the multilateral collaborative modified, TiO2-Pt/CCF has higher catalytic activity than noporous TiO2/CCF and mesoporous TiO2/CCF.
Based on employing the TiCl4, cetyltrimethyl ammonium bromide, chloroplatinic acid and conductive carbon felt as titanium source, template agent, doping-ion and carrier, respectively, the precursor solution of liquid crystal-Pt ion-inorganic titanium was prepared by hydrothermal synthesis method. The photoelectrode of Pt doped mesoporous TiO2/conductive carbon felt (TiO2-Pt/CCF) was obtained by the dip-coating method with the aid of ultrasonic system under nitrogen protection. The obtained TiO2-Pt/CCF was characterized by modern analytical tools. The photoelectrocatalytic performance of material was analyzed by degradation of benzaldehyde, and the photoelectrocatalytic synergistic mechanism was analyzed. The results show that the mesoporous processing can increase the specific surface area of TiO2-Pt/CCF, enlarge the degradation reaction area, and increase the concentration of catalyst surface degradation product; the metal ion doping can bring impurity level, reduce the band gap of TiO2, at the same time, Pt acts as a photo-electron and hole trap, and inhibits the electron and hole recombine, improves the photoelectrocatalytic activity of TiO2-Pt/CCF; the TiO2 loading can enhance the absorption and the surface electron transfer of target degradation product. Under the multilateral collaborative modified, TiO2-Pt/CCF has higher catalytic activity than noporous TiO2/CCF and mesoporous TiO2/CCF.
2016, 33(12): 2905-2910.
doi: 10.13801/j.cnki.fhclxb.20160219.004
Abstract:
Due to the sodium ion radius is 70% larger than lithium ion radius, the embedding for sodium ion in and out of the graphite electrode materials is more difficult, and the graphite material needs to be modified. Using the natural graphite as raw material, graphene oxide was prepared via the Hummers method. Using the tetra-n-butyl titanate as raw material on this basis, the precursor TiO2/graphene oxide (TiO2/GO) composite was prepared by sol-gel method, and the anatase type TiO2/reduced graphene oxide (TiO2/RGO) composite was obtained by heat treatment. The electrochemical test results show that when TiO2 content is 15wt%, the TiO2/RGO composites exhibit an initial discharge specific capacity of 74.08 mAh·g-1 at current density of 20 mA·g-1. And with the increase of the number of cycles, the discharge specific capacity gradually increases, and reaches 109.10 mAh·g-1 after 50 cycles, and the charge-discharge efficiency is 65.59% after 50 cycles, which is also showing a trend of increasing. While the initial discharge specific capacity of pure reduction oxidation graphite is 41.43 mAh·g-1, and reaches 20.47 mAh·g-1 after 50 cycles.
Due to the sodium ion radius is 70% larger than lithium ion radius, the embedding for sodium ion in and out of the graphite electrode materials is more difficult, and the graphite material needs to be modified. Using the natural graphite as raw material, graphene oxide was prepared via the Hummers method. Using the tetra-n-butyl titanate as raw material on this basis, the precursor TiO2/graphene oxide (TiO2/GO) composite was prepared by sol-gel method, and the anatase type TiO2/reduced graphene oxide (TiO2/RGO) composite was obtained by heat treatment. The electrochemical test results show that when TiO2 content is 15wt%, the TiO2/RGO composites exhibit an initial discharge specific capacity of 74.08 mAh·g-1 at current density of 20 mA·g-1. And with the increase of the number of cycles, the discharge specific capacity gradually increases, and reaches 109.10 mAh·g-1 after 50 cycles, and the charge-discharge efficiency is 65.59% after 50 cycles, which is also showing a trend of increasing. While the initial discharge specific capacity of pure reduction oxidation graphite is 41.43 mAh·g-1, and reaches 20.47 mAh·g-1 after 50 cycles.
2016, 33(12): 2911-2917.
doi: 10.13801/j.cnki.fhclxb.20160317.005
Abstract:
A micromechanics model was developed to characterize the effective creep response and macroscopic stress-strain behavior of linear viscoelastic polymer matrix composites based on variational asymptotic homogenization theory framework. Stated from the energy functional variational expression derived from the constitutive equations of the linear viscoelastic polymer matrix composites, the effective creep compliance coefficients of the linear viscoelastic polymer matrix composites were solved by using the variational asymptotic method. On this basis, the time-dependent and uniaxial tensile behavior of polymer matrix composites were calculated. The applicability and accuracy of the model were verified by numerical examples. Since all calculations were accomplished in the time domain, the Laplace transform and inversion commonly used for linearly viscoelastic composites are not needed in this theory, and the computational efficiency is greatly improved.
A micromechanics model was developed to characterize the effective creep response and macroscopic stress-strain behavior of linear viscoelastic polymer matrix composites based on variational asymptotic homogenization theory framework. Stated from the energy functional variational expression derived from the constitutive equations of the linear viscoelastic polymer matrix composites, the effective creep compliance coefficients of the linear viscoelastic polymer matrix composites were solved by using the variational asymptotic method. On this basis, the time-dependent and uniaxial tensile behavior of polymer matrix composites were calculated. The applicability and accuracy of the model were verified by numerical examples. Since all calculations were accomplished in the time domain, the Laplace transform and inversion commonly used for linearly viscoelastic composites are not needed in this theory, and the computational efficiency is greatly improved.
2016, 33(12): 2918-2930.
doi: 10.13801/j.cnki.fhclxb.20160411.001
Abstract:
Considering the fact that the design parameters for bolted joint in T800 grade composites are extremely scarce in China, a joint strength prediction strategy substituting the tests was developed to save research time period and cost. This proposed strategy is a combination of the continuum damage mechanics (CDM) and engineering approach. First, in this strength prediction strategy, CDM finite element model for the test specimen was utilized to determine the design parameters for bolted joint structure, such as modified bearing strength parameter for single-lap, composite bolted joint, un-notched laminate tensile strength and stress concentration relief factor. Then, based on these design parameters, an efficient engineering algorithm was established to obtain the ultimate bearing strength of single-lap, composite bolted joints. It can be found that the design parameters and strength estimation results for bolted joint in T800 grade composites based on this strategy show excellent agreement with the test results. This demonstrates the strategy is feasible.
Considering the fact that the design parameters for bolted joint in T800 grade composites are extremely scarce in China, a joint strength prediction strategy substituting the tests was developed to save research time period and cost. This proposed strategy is a combination of the continuum damage mechanics (CDM) and engineering approach. First, in this strength prediction strategy, CDM finite element model for the test specimen was utilized to determine the design parameters for bolted joint structure, such as modified bearing strength parameter for single-lap, composite bolted joint, un-notched laminate tensile strength and stress concentration relief factor. Then, based on these design parameters, an efficient engineering algorithm was established to obtain the ultimate bearing strength of single-lap, composite bolted joints. It can be found that the design parameters and strength estimation results for bolted joint in T800 grade composites based on this strategy show excellent agreement with the test results. This demonstrates the strategy is feasible.
2016, 33(12): 2931-2940.
doi: 10.13801/j.cnki.fhclxb.20160321.002
Abstract:
Plain concrete, steel fiber and hybrid fiber reinforced ultra-high-performance concretes, with 140-160 MPa compressive strength at 56 d, were prepared using common raw materials. The residual compressive strength and tensile splitting strength of these concretes after exposure to high temperature were determined experimentally. Explosive spalling test was carried out on the specimens with 100% moisture content and two heating rates were employed to study the effect of heating rate on spalling behavior of ultra-high-performance concrete. The results indicate that residual compressive strength of each type of concrete increases firstly, and then decreases with increasing temperature. After exposure to 800℃, residual compressive strength is approximately 30% of that at normal temperature. Residual tensile splitting strength of both steel fiber reinforced concrete and hybrid fiber reinforced concrete also increase firstly and then decrease, which are 15.1% and 35.4% of the original strength, respectively. Residual tensile splitting strength of plain concrete decreases with increasing temperature, which is 20.3% of its original strength after exposure to 800℃. At 7.5℃/min heating rate, explosive spalling of each type of concrete specimens with 100% moisture content is quite severe. Nevertheless, steel fiber can alleviate explosive spalling but does not avoid the occurrence of explosive spalling, and the effect of hybrid fiber on improving spalling resistance behavior of ultra-high-performance concrete is not significantly superior to that of steel fiber. At 2.5℃/min heating rate, incorporating hybrid fiber inhibits the occurrence of explosive spalling in some specimens.
Plain concrete, steel fiber and hybrid fiber reinforced ultra-high-performance concretes, with 140-160 MPa compressive strength at 56 d, were prepared using common raw materials. The residual compressive strength and tensile splitting strength of these concretes after exposure to high temperature were determined experimentally. Explosive spalling test was carried out on the specimens with 100% moisture content and two heating rates were employed to study the effect of heating rate on spalling behavior of ultra-high-performance concrete. The results indicate that residual compressive strength of each type of concrete increases firstly, and then decreases with increasing temperature. After exposure to 800℃, residual compressive strength is approximately 30% of that at normal temperature. Residual tensile splitting strength of both steel fiber reinforced concrete and hybrid fiber reinforced concrete also increase firstly and then decrease, which are 15.1% and 35.4% of the original strength, respectively. Residual tensile splitting strength of plain concrete decreases with increasing temperature, which is 20.3% of its original strength after exposure to 800℃. At 7.5℃/min heating rate, explosive spalling of each type of concrete specimens with 100% moisture content is quite severe. Nevertheless, steel fiber can alleviate explosive spalling but does not avoid the occurrence of explosive spalling, and the effect of hybrid fiber on improving spalling resistance behavior of ultra-high-performance concrete is not significantly superior to that of steel fiber. At 2.5℃/min heating rate, incorporating hybrid fiber inhibits the occurrence of explosive spalling in some specimens.
2016, 33(12): 2941-2951.
doi: 10.13801/j.cnki.fhclxb.20160302.001
Abstract:
Sodium thiosulfate pentahydrate(Na2S2O3·5H2O) phase change energy storage material has high phase change latent heat, energy storage density, etc. However, Na2S2O3·5H2O has undercooling and phase separation, the performance is unstable. Adding the nucleating agent K2SO4, CaSO4·2H2O, Na4P2O7·10H2O and enhance heat transfer material expanded graphite(EG) could improve the performance, EG/Na2S2O3·5H2O phase change energy storage composite with stable properties was prepared. Test results show that the nucleation performance of K2SO4 for Na2S2O3·5H2O is worse, both CaSO4·2H2O and Na4P2O7·10H2O have better nucleation performance, which could significantly reduce the undercooling degree of Na2S2O3·5H2O. However, the CaSO4·2H2O system is unstable, adding the mass fraction 3.0% of Na4P2O7·10H2O could reduce the undercooling degree of Na2S2O3·5H2O to within 1℃, adding mass fraction 0.5%-2.0% of EG could reduce the undercooling degree to about 2℃, and mass fraction 7% of EG can completely eliminate phase separation of the system. Therefore, the optimal composition for phase change materials is 7.0% of EG, 3.0% of Na4P2O7·10H2O, and 90.0% of Na2S2O3·5H2O. The latent heat of EG/Na4P2O7·10H2O/Na2S2O3·5H2O composite is 192.5 kJ·kg-1. No liquid leakage and no phase separation when the phase transition. The thermal storage time is shorter 22.3% than pure substance, and heat release faster.
Sodium thiosulfate pentahydrate(Na2S2O3·5H2O) phase change energy storage material has high phase change latent heat, energy storage density, etc. However, Na2S2O3·5H2O has undercooling and phase separation, the performance is unstable. Adding the nucleating agent K2SO4, CaSO4·2H2O, Na4P2O7·10H2O and enhance heat transfer material expanded graphite(EG) could improve the performance, EG/Na2S2O3·5H2O phase change energy storage composite with stable properties was prepared. Test results show that the nucleation performance of K2SO4 for Na2S2O3·5H2O is worse, both CaSO4·2H2O and Na4P2O7·10H2O have better nucleation performance, which could significantly reduce the undercooling degree of Na2S2O3·5H2O. However, the CaSO4·2H2O system is unstable, adding the mass fraction 3.0% of Na4P2O7·10H2O could reduce the undercooling degree of Na2S2O3·5H2O to within 1℃, adding mass fraction 0.5%-2.0% of EG could reduce the undercooling degree to about 2℃, and mass fraction 7% of EG can completely eliminate phase separation of the system. Therefore, the optimal composition for phase change materials is 7.0% of EG, 3.0% of Na4P2O7·10H2O, and 90.0% of Na2S2O3·5H2O. The latent heat of EG/Na4P2O7·10H2O/Na2S2O3·5H2O composite is 192.5 kJ·kg-1. No liquid leakage and no phase separation when the phase transition. The thermal storage time is shorter 22.3% than pure substance, and heat release faster.
2016, 33(12): 2952-2960.
doi: 10.13801/j.cnki.fhclxb.20160315.003
Abstract:
We studied the influence and mechanism of external factors including activator and curing temperature on the mechanical properties of geopoylmer. NaOH and Na2SiO3 were used as the activator. And the sensitivity of the mechanical properties of metakaolin-based geopolymer to the activator modulus, the activator concentration, the curing temperature, and the curing time was analyzed by orthogonal tests. The mechanism of the activator concentration influencing geopolymerization and synthetics properties was investigated by the microcalorimetric, infrared spectrum and scanning electron microscope-energy disperse spectroscopy. The test results show that the concentration of activator is the most important factor for mechanical properties of geopolymer. The compressive strength of geopolymer increases with the increase of the activator concentration. The activator modulus ranks second, the increase in which results in the decrease of the geopolymer strength. Higher degree of polymerization is obtained when the concentration of activator increases. The polymerization reaction tends to full completion and mechanical properties of geopolymer increase subsequently, the strength of geopolymer increases to 99.98 MPa when the activator concentration reaches 80%, moreover the ratio of silicon to aluminium is greater than 1.
We studied the influence and mechanism of external factors including activator and curing temperature on the mechanical properties of geopoylmer. NaOH and Na2SiO3 were used as the activator. And the sensitivity of the mechanical properties of metakaolin-based geopolymer to the activator modulus, the activator concentration, the curing temperature, and the curing time was analyzed by orthogonal tests. The mechanism of the activator concentration influencing geopolymerization and synthetics properties was investigated by the microcalorimetric, infrared spectrum and scanning electron microscope-energy disperse spectroscopy. The test results show that the concentration of activator is the most important factor for mechanical properties of geopolymer. The compressive strength of geopolymer increases with the increase of the activator concentration. The activator modulus ranks second, the increase in which results in the decrease of the geopolymer strength. Higher degree of polymerization is obtained when the concentration of activator increases. The polymerization reaction tends to full completion and mechanical properties of geopolymer increase subsequently, the strength of geopolymer increases to 99.98 MPa when the activator concentration reaches 80%, moreover the ratio of silicon to aluminium is greater than 1.
