2017 Vol. 34, No. 3
2017, 34(3): 471-485.
doi: 10.13801/j.cnki.fhclxb.20170105.001
Abstract:
Cure-induced distortions and residual stresses influence application of composites. Accurate prediction for cure-induced distortions and residual stresses can provide a basis for adjustment of composites structure and process design to reduce the cure-induced distortions and residual stresses. Numerical simulation method was widely adopted due to its simplicity and high prediction accuracy. The sub-models of heat transfer-cure, flow-consolidation and stress-distortion in numerical simulation for cure-induced distortions and residuals stresses in composites were mainly introduced, with a particular emphasis being on state-of-the-art research on the constitutive law and tool-part interaction in the sub-model of stress-distortion. This paper aims at proposing the orientation and reference for the prediction of cure-induced distortions and residual stresses. The future development of cure-induced distortions and residual stresses was discussed.
Cure-induced distortions and residual stresses influence application of composites. Accurate prediction for cure-induced distortions and residual stresses can provide a basis for adjustment of composites structure and process design to reduce the cure-induced distortions and residual stresses. Numerical simulation method was widely adopted due to its simplicity and high prediction accuracy. The sub-models of heat transfer-cure, flow-consolidation and stress-distortion in numerical simulation for cure-induced distortions and residuals stresses in composites were mainly introduced, with a particular emphasis being on state-of-the-art research on the constitutive law and tool-part interaction in the sub-model of stress-distortion. This paper aims at proposing the orientation and reference for the prediction of cure-induced distortions and residual stresses. The future development of cure-induced distortions and residual stresses was discussed.
2017, 34(3): 486-493.
doi: 10.13801/j.cnki.fhclxb.20160607.002
Abstract:
A kind of nano-SiO2/PLA meltblown chip, composited with the surface modified nano-SiO2 electret and PLA resin, was prepared by two-screw extruder. After meltblown manufacturing, the nano-SiO2/PLA compo-site meltblown nonwovens were obtained. FTIR testing was used to evaluate the effect of surface modification of nano-SiO2. DSC testing was used to investigate the crystallinity of nano-SiO2/PLA meltblown chips at fast cooling process like melt-blowing. Filter media testing platform and SEM testing were used to investigate the filtration property and micromorphology of the nano-SiO2/PLA composite meltblown nonwovens respectively. The mass loss method was used to evaluate the degradation property of the nano-SiO2/PLA composite meltblown nonwovens in the end. The results show that after modification the surface of nano-SiO2 has been covered with organic functional groups. At 100℃/min cooling rate, the crystallinity of neat PLA is quite low while adding nano-SiO2 electret can remarkably improve it. A small amount addition of nano-SiO2 electret can notably enhance the filtration efficiency of PLA composite meltblown nonwovens, as the composite with 0.75 wt% nano-SiO2 has a high filtration efficiency of 99.69%, which is close to the commercialized high efficiency particulate air filter (HEPA) level PP product. The nano-SiO2/PLA composite meltblown nonwovens are degradable at neutral hydrolysis condition, of which the mass drop to 79.57% after 8 months degrading.
A kind of nano-SiO2/PLA meltblown chip, composited with the surface modified nano-SiO2 electret and PLA resin, was prepared by two-screw extruder. After meltblown manufacturing, the nano-SiO2/PLA compo-site meltblown nonwovens were obtained. FTIR testing was used to evaluate the effect of surface modification of nano-SiO2. DSC testing was used to investigate the crystallinity of nano-SiO2/PLA meltblown chips at fast cooling process like melt-blowing. Filter media testing platform and SEM testing were used to investigate the filtration property and micromorphology of the nano-SiO2/PLA composite meltblown nonwovens respectively. The mass loss method was used to evaluate the degradation property of the nano-SiO2/PLA composite meltblown nonwovens in the end. The results show that after modification the surface of nano-SiO2 has been covered with organic functional groups. At 100℃/min cooling rate, the crystallinity of neat PLA is quite low while adding nano-SiO2 electret can remarkably improve it. A small amount addition of nano-SiO2 electret can notably enhance the filtration efficiency of PLA composite meltblown nonwovens, as the composite with 0.75 wt% nano-SiO2 has a high filtration efficiency of 99.69%, which is close to the commercialized high efficiency particulate air filter (HEPA) level PP product. The nano-SiO2/PLA composite meltblown nonwovens are degradable at neutral hydrolysis condition, of which the mass drop to 79.57% after 8 months degrading.
2017, 34(3): 494-500.
doi: 10.13801/j.cnki.fhclxb.20160606.003
Abstract:
Ablation behaviors of 2D braided carbon fiber/epoxy composite irradiated by fiber laser were investigated. Ablation characteristics of braided composites under different thermal flux conditions were obtained and the laser ablation mechanism was analyzed. Combined with non-contact temperature measurement and contact temperature measurement, the transient temperature field evolution of the surface of the composite was measured by the high temperature infrared camera, while the temperature history of back surface was obtained by thermocouple. The experiment results show that when the level of incident laser power density is 102 W·cm-2, the epoxy resin of the 2D braided composites has obvious mass transfer, but the morphology of the carbon fiber is not changed. Meanwhile under high-energy laser irradiation, the temperature difference between the front and back surface of 2D braided carbon fiber/epoxy composites is very large. The maximum temperature of the front surface is close to 2 000℃, and the maximum temperature of the back surface is between 200-500℃.
Ablation behaviors of 2D braided carbon fiber/epoxy composite irradiated by fiber laser were investigated. Ablation characteristics of braided composites under different thermal flux conditions were obtained and the laser ablation mechanism was analyzed. Combined with non-contact temperature measurement and contact temperature measurement, the transient temperature field evolution of the surface of the composite was measured by the high temperature infrared camera, while the temperature history of back surface was obtained by thermocouple. The experiment results show that when the level of incident laser power density is 102 W·cm-2, the epoxy resin of the 2D braided composites has obvious mass transfer, but the morphology of the carbon fiber is not changed. Meanwhile under high-energy laser irradiation, the temperature difference between the front and back surface of 2D braided carbon fiber/epoxy composites is very large. The maximum temperature of the front surface is close to 2 000℃, and the maximum temperature of the back surface is between 200-500℃.
2017, 34(3): 501-507.
doi: 10.13801/j.cnki.fhclxb.20160526.004
Abstract:
In order to quantitatively characterize the interphase of carbon fiber reinforced polymer composites, in situ peak force quantitative nano-mechanics (PF-QNM) technique was introduced. Its general principles, calibration method and applicability were analyzed. PF-QNM technique was used to measure the interphase dimensions and in situ modulus of each component of carbon fiber/poly-ether-ether-ketone (T300/PEEK), carbon fiber/poly-ether-sulfone (T300/PES) and carbon fiber/epoxy (T700/TR1219B). The results show that this technique can determine the width and elastic modulus of the interphase in nanoscale lateral resolution. The gradient increases of modulus exist in the three composites from the matrix region to carbon fiber region. The interphase thicknesses of T300/PEEK, T300/PES and T700/TR1219B are (69.3±7.9)nm,(101.3±10.2)nm and (48.4±5.4)nm, respectively. In this study, the interphase thickness of thermoset composites is smaller than that of thermoplastic composites. The statistical analysis shows that the average modulus of resin matrix of T300/PEEK, T300/PES and T700/TR1219B are 4.36 GPa, 4.96 GPa and 3.59 GPa, respectively, which is close to their elastic modulus in bulk materials.
In order to quantitatively characterize the interphase of carbon fiber reinforced polymer composites, in situ peak force quantitative nano-mechanics (PF-QNM) technique was introduced. Its general principles, calibration method and applicability were analyzed. PF-QNM technique was used to measure the interphase dimensions and in situ modulus of each component of carbon fiber/poly-ether-ether-ketone (T300/PEEK), carbon fiber/poly-ether-sulfone (T300/PES) and carbon fiber/epoxy (T700/TR1219B). The results show that this technique can determine the width and elastic modulus of the interphase in nanoscale lateral resolution. The gradient increases of modulus exist in the three composites from the matrix region to carbon fiber region. The interphase thicknesses of T300/PEEK, T300/PES and T700/TR1219B are (69.3±7.9)nm,(101.3±10.2)nm and (48.4±5.4)nm, respectively. In this study, the interphase thickness of thermoset composites is smaller than that of thermoplastic composites. The statistical analysis shows that the average modulus of resin matrix of T300/PEEK, T300/PES and T700/TR1219B are 4.36 GPa, 4.96 GPa and 3.59 GPa, respectively, which is close to their elastic modulus in bulk materials.
2017, 34(3): 508-514.
doi: 10.13801/j.cnki.fhclxb.20160511.005
Abstract:
Bronze-Sm2O3/epoxy-modified silicone composite coatings were prepared through spraying method by using epoxy modified silicone and bronze & Sm2O3 as adhesives and pigments, respectively. The effect of heat treatment temperature and heat treatment time on the appearance, microstructure, near-infrared reflectivity, infrared emissivity, and mechanical properties of the as-prepared coatings were systematical investigated. The results indicate that the maximum withstand temperature of bronze-Sm2O3/epoxy modified silicone composite coatings can reach 300℃. After heat treatment at 300℃ with 5 h, the appearance and microstructure of the coatings are almost the same. The emissivity and near-infrared reflectivity at 1.06 μm can be as low as 0.590 and 57.4%, respectively. The mechanical properties remain intact. The hardness, adhesion strength, and impact strength can be maintained at 4 H, 1 grade, and 50 kg·cm, respectively. The prepared coatings can be used long-term at 250℃. After heat treatment at 250℃ with 100 h, the appearance and microstructure of the coatings remain unchanged. The emissivity and near-infrared reflectivity at 1.06 μm can be as low as 0.558 and 59.3%, respectively. The mechanical properties remain intact. The hardness, adhesion strength, and impact strength can be maintained at 4 H, 1 grade, and 50 kg·cm, respectively.
Bronze-Sm2O3/epoxy-modified silicone composite coatings were prepared through spraying method by using epoxy modified silicone and bronze & Sm2O3 as adhesives and pigments, respectively. The effect of heat treatment temperature and heat treatment time on the appearance, microstructure, near-infrared reflectivity, infrared emissivity, and mechanical properties of the as-prepared coatings were systematical investigated. The results indicate that the maximum withstand temperature of bronze-Sm2O3/epoxy modified silicone composite coatings can reach 300℃. After heat treatment at 300℃ with 5 h, the appearance and microstructure of the coatings are almost the same. The emissivity and near-infrared reflectivity at 1.06 μm can be as low as 0.590 and 57.4%, respectively. The mechanical properties remain intact. The hardness, adhesion strength, and impact strength can be maintained at 4 H, 1 grade, and 50 kg·cm, respectively. The prepared coatings can be used long-term at 250℃. After heat treatment at 250℃ with 100 h, the appearance and microstructure of the coatings remain unchanged. The emissivity and near-infrared reflectivity at 1.06 μm can be as low as 0.558 and 59.3%, respectively. The mechanical properties remain intact. The hardness, adhesion strength, and impact strength can be maintained at 4 H, 1 grade, and 50 kg·cm, respectively.
2017, 34(3): 515-521.
doi: 10.13801/j.cnki.fhclxb.20160511.006
Abstract:
The traditional mixing process of polyvinyl chloride (PVC) slush molding powder was improved by adding mixing phase at room temperature and optimizing the key processing parameters of the new phase. Different influences on the homodisperse of inorganic nanoparticles between the new process and the traditional process were compared using active CaCO3 with particle sizes of 60-80 nm and rutile titanium dioxide with particle sizes of 100-120 nm as raw materials. Besides, the effects of different process parameters of mixing at room temperature on material properties such as the fluidity of slush molding powder, mechanical property and thermostability of slush molded skins were analyzed quantitatively. The results show that the optimized mixing process can enhance the uniform dispersibility of nanoparticles in PVC slush molded skins and the fluidity of PVC slush molding powder, and it can improve the elongation at break, thermostability and resistance of hot air loss of PVC slush molded skins.
The traditional mixing process of polyvinyl chloride (PVC) slush molding powder was improved by adding mixing phase at room temperature and optimizing the key processing parameters of the new phase. Different influences on the homodisperse of inorganic nanoparticles between the new process and the traditional process were compared using active CaCO3 with particle sizes of 60-80 nm and rutile titanium dioxide with particle sizes of 100-120 nm as raw materials. Besides, the effects of different process parameters of mixing at room temperature on material properties such as the fluidity of slush molding powder, mechanical property and thermostability of slush molded skins were analyzed quantitatively. The results show that the optimized mixing process can enhance the uniform dispersibility of nanoparticles in PVC slush molded skins and the fluidity of PVC slush molding powder, and it can improve the elongation at break, thermostability and resistance of hot air loss of PVC slush molded skins.
2017, 34(3): 522-529.
doi: 10.13801/j.cnki.fhclxb.20161202.007
Abstract:
The influence of single layer ZnSnO3@Mg(OH)2 microcapsule and double layer ZnSnO3@Mg(OH)2@melamine formaldehyde resin(MF) microcapsule on the flame retardancy and smoke suppression properties of polyvinyl chloride(PVC) membranes were analyzed by limiting oxygen index(LOI), horizontal and vertical burning test, smoke density(SDR) test, SEM and TG instrument. The results show that ZnSnO3@Mg(OH)2 and ZnSnO3@Mg(OH)2@MFm icrocapsules can effectively enhance the flame retardancy, smoke suppression, anti-dripping and self-extinguishing properties of PVC membranes. The LOI value of ZnSnO3@Mg(OH)2/PVC and ZnSnO3@Mg(OH)2@MF/PVC membrane composites obviously increases, with increasing the content of the microcapsules. However, when the content of the microcapsules increases, the smoke density and self-extinguishing time of ZnSnO3@Mg(OH)2/PVC and ZnSnO3@Mg(OH)2@MF/PVC membrane composites decreases. The TG results show that the initial degradation temperature of ZnSnO3@Mg(OH)2/PVC and ZnSnO3@Mg(OH)2@MF/PVC membrane composites move to low temperature and the amount of residual carbon increases with the content of the microcapsules. The SEM micrographs of residual carbon of ZnSnO3@Mg(OH)2/PVC and ZnSnO3@Mg(OH)2@MF/PVC membrane composites show that the addition of the microcapsules effectively promotes the form compact carbon layer of ZnSnO3@Mg(OH)2/PVC and ZnSnO3@Mg(OH)2@MF/PVC membrane composites during burning, which not only can inhibit oxygen and heat to go into the PVC bulk, but also inhibit combustion gases to go out the PVC bulk. SEM and tensile strength results show that double layer microcapsule can availably improve the dispersion and compatibility between inorganic particles and PVC matrix.
The influence of single layer ZnSnO3@Mg(OH)2 microcapsule and double layer ZnSnO3@Mg(OH)2@melamine formaldehyde resin(MF) microcapsule on the flame retardancy and smoke suppression properties of polyvinyl chloride(PVC) membranes were analyzed by limiting oxygen index(LOI), horizontal and vertical burning test, smoke density(SDR) test, SEM and TG instrument. The results show that ZnSnO3@Mg(OH)2 and ZnSnO3@Mg(OH)2@MFm icrocapsules can effectively enhance the flame retardancy, smoke suppression, anti-dripping and self-extinguishing properties of PVC membranes. The LOI value of ZnSnO3@Mg(OH)2/PVC and ZnSnO3@Mg(OH)2@MF/PVC membrane composites obviously increases, with increasing the content of the microcapsules. However, when the content of the microcapsules increases, the smoke density and self-extinguishing time of ZnSnO3@Mg(OH)2/PVC and ZnSnO3@Mg(OH)2@MF/PVC membrane composites decreases. The TG results show that the initial degradation temperature of ZnSnO3@Mg(OH)2/PVC and ZnSnO3@Mg(OH)2@MF/PVC membrane composites move to low temperature and the amount of residual carbon increases with the content of the microcapsules. The SEM micrographs of residual carbon of ZnSnO3@Mg(OH)2/PVC and ZnSnO3@Mg(OH)2@MF/PVC membrane composites show that the addition of the microcapsules effectively promotes the form compact carbon layer of ZnSnO3@Mg(OH)2/PVC and ZnSnO3@Mg(OH)2@MF/PVC membrane composites during burning, which not only can inhibit oxygen and heat to go into the PVC bulk, but also inhibit combustion gases to go out the PVC bulk. SEM and tensile strength results show that double layer microcapsule can availably improve the dispersion and compatibility between inorganic particles and PVC matrix.
2017, 34(3): 530-539.
doi: 10.13801/j.cnki.fhclxb.20160523.008
Abstract:
The solid state shear milling (S3M) followed by melt mixing process was applied to prepare Al/linear low-density polyethylene (LLDPE) composites with high performance. The effects of S3M pretreatment on the microstructure, crystallization, thermal stability, rheological behaviour, thermal conductivity and mechanical properties of the Al/LLDPE composites were systematically investigated. The results indicate the spherical Al particulates are squeezed into flakes during compounding with LLDPE by S3M, and their dispersion and interfacial adhesion are improved as well. Furthermore, the flaky Al with high radius-thickness ratio can be easier to form thermal network and orientation during processing especially at high filler loading. Consequently, the Al/LLDPE composites with S3M pretreatment show better crystallization and thermal properties, lower rheological percolation threshold, higher thermal conductivity and superior mechanical properties than Al/LLDPE composites prepared by conventional melt mixing. In particular, the rheological percolation phenomena of the composites with S3M pretreatment is observed around at 15% mass fraction of Al. When the mass fraction of Al is 80%, the thermal conductivity of Al/LLDPE composite with S3M pretreatment is as high as 8.86 W/(m·K), and its the tensile strength and flexural strength respectively are 33.0 MPa and 31.2 MPa, much higher than those of the untreated composite. And a significant increase of 13℃ in the onset temperature of degradation is also observed.
The solid state shear milling (S3M) followed by melt mixing process was applied to prepare Al/linear low-density polyethylene (LLDPE) composites with high performance. The effects of S3M pretreatment on the microstructure, crystallization, thermal stability, rheological behaviour, thermal conductivity and mechanical properties of the Al/LLDPE composites were systematically investigated. The results indicate the spherical Al particulates are squeezed into flakes during compounding with LLDPE by S3M, and their dispersion and interfacial adhesion are improved as well. Furthermore, the flaky Al with high radius-thickness ratio can be easier to form thermal network and orientation during processing especially at high filler loading. Consequently, the Al/LLDPE composites with S3M pretreatment show better crystallization and thermal properties, lower rheological percolation threshold, higher thermal conductivity and superior mechanical properties than Al/LLDPE composites prepared by conventional melt mixing. In particular, the rheological percolation phenomena of the composites with S3M pretreatment is observed around at 15% mass fraction of Al. When the mass fraction of Al is 80%, the thermal conductivity of Al/LLDPE composite with S3M pretreatment is as high as 8.86 W/(m·K), and its the tensile strength and flexural strength respectively are 33.0 MPa and 31.2 MPa, much higher than those of the untreated composite. And a significant increase of 13℃ in the onset temperature of degradation is also observed.
2017, 34(3): 540-549.
doi: 10.13801/j.cnki.fhclxb.20160616.009
Abstract:
A strategy was proposed to proceed the secondary fine processing when the cutting tool returned by fully taking advantage of eccentricity machining feature of orbital drilling. The effect laws of return processing parameters to machining quality and precision of the stacked materials were researched by conducting orthogonal experiments, and the resultant optimized machining parameters were determined. The experiment results show that optimized return machining process can improve hole accuracy of CFRP/Ti-6Al-4V stacks and avoid the scratch defects of the hole wall of CFRP. An average value of CFRP hole roughness decreases from Ra3.52 to Ra1.31. Less tear formation occur at the CFRP hole entry and no burrs forms at the Ti-6Al-4V hole exit.
A strategy was proposed to proceed the secondary fine processing when the cutting tool returned by fully taking advantage of eccentricity machining feature of orbital drilling. The effect laws of return processing parameters to machining quality and precision of the stacked materials were researched by conducting orthogonal experiments, and the resultant optimized machining parameters were determined. The experiment results show that optimized return machining process can improve hole accuracy of CFRP/Ti-6Al-4V stacks and avoid the scratch defects of the hole wall of CFRP. An average value of CFRP hole roughness decreases from Ra3.52 to Ra1.31. Less tear formation occur at the CFRP hole entry and no burrs forms at the Ti-6Al-4V hole exit.
2017, 34(3): 550-556.
doi: 10.13801/j.cnki.fhclxb.20160426.010
Abstract:
The comprehensive experimental investigations are conducted on the compressive fatigue resistant of polyurethane grout materials, which are widely used in maintenance of infrastructure and subjected to repeated loads. SEM and compression fatigue tests were applied to the specimens with different densities. The variation of strain under the cyclic compressive load is recorded. The test results show that strain development under load cycles can be divided into three stages:the first stage lasts for decades of cycles and elastic strain increases gradually; the strain at second stage is relative stable; while at third stage, specimen would be fatigue failure at higher stress level and behave as cyclic hardening at lower stress level. The stress threshold of fatigue, α,is between 0.7 and 0.8 for the specimen of 0.3 g/cm3, and it is between 0.6 and 0.7 for the specimen of 0.5 g/cm3. When fatigue failure happens, the specimen will be bulging perpendicular of the load. Developing of micro cracks in polymer walls and bulking of polymer struts can be observed in microscope images. Besides, a parameter D based on the variation of elastic modulus under cycle loading is proposed to quantify the fatigue failure, and D is more pronounced than strain index when materials undergo cyclic hardening at the third stage at low level.
The comprehensive experimental investigations are conducted on the compressive fatigue resistant of polyurethane grout materials, which are widely used in maintenance of infrastructure and subjected to repeated loads. SEM and compression fatigue tests were applied to the specimens with different densities. The variation of strain under the cyclic compressive load is recorded. The test results show that strain development under load cycles can be divided into three stages:the first stage lasts for decades of cycles and elastic strain increases gradually; the strain at second stage is relative stable; while at third stage, specimen would be fatigue failure at higher stress level and behave as cyclic hardening at lower stress level. The stress threshold of fatigue, α,is between 0.7 and 0.8 for the specimen of 0.3 g/cm3, and it is between 0.6 and 0.7 for the specimen of 0.5 g/cm3. When fatigue failure happens, the specimen will be bulging perpendicular of the load. Developing of micro cracks in polymer walls and bulking of polymer struts can be observed in microscope images. Besides, a parameter D based on the variation of elastic modulus under cycle loading is proposed to quantify the fatigue failure, and D is more pronounced than strain index when materials undergo cyclic hardening at the third stage at low level.
2017, 34(3): 557-563.
doi: 10.13801/j.cnki.fhclxb.20160523.011
Abstract:
Comparison analysis on bearing strength of two thickness composite laminates with countersunk bolt joint or protruding bolt joint was conducted using experimental method to deal with the strength and damage evolution of mid-thick composite laminates with countersunk bolt joints. The results provide sufficient evidence that the decrease of bearing strength caused by the laminates thickness increase of countersunk bolt is less than that of protruding bolt connection structure. To investigate the damage evolution and failure strength of countersunk bolt joint, a new continuum damage failure model with the combination of continuum damage evolution and 3D mixed failure criterions was proposed. The model takes the advantages of consideration of matrix shear nonlinearity, using the improved fiber failure criterion and improvement in the convergence of the composite structure. The predicted results agree well with the experimental results and the deviation of the failure strength is no more than 8.62%.
Comparison analysis on bearing strength of two thickness composite laminates with countersunk bolt joint or protruding bolt joint was conducted using experimental method to deal with the strength and damage evolution of mid-thick composite laminates with countersunk bolt joints. The results provide sufficient evidence that the decrease of bearing strength caused by the laminates thickness increase of countersunk bolt is less than that of protruding bolt connection structure. To investigate the damage evolution and failure strength of countersunk bolt joint, a new continuum damage failure model with the combination of continuum damage evolution and 3D mixed failure criterions was proposed. The model takes the advantages of consideration of matrix shear nonlinearity, using the improved fiber failure criterion and improvement in the convergence of the composite structure. The predicted results agree well with the experimental results and the deviation of the failure strength is no more than 8.62%.
2017, 34(3): 564-573.
doi: 10.13801/j.cnki.fhclxb.20160511.012
Abstract:
A series of equivalent simplified methods were investigated in this paper and equivalent parameters were calculated for sandwich plate with polyurethane elastomer core reinforced by crossing walls. Firstly, a global equivalent method was discussed in case of ignoring the shear deformation of the core. In this way, the reinforced structure could be made equivalence to orthotropic thin plate and stiffness coefficients equations were presented. Secondly, when considering shear deformation of the core, equivalent elastic coefficients of the core compounded by crossing walls and polyurethane elastomers were also given by theoretical derivation. Finally, the equivalent orthotropic modules for the polyurethane core with crossing walls were analyzed by finite element method (FEM) based on equivalent strain energy density. And the results show that the error between theoretical derivation and FEM is less than 10%.
A series of equivalent simplified methods were investigated in this paper and equivalent parameters were calculated for sandwich plate with polyurethane elastomer core reinforced by crossing walls. Firstly, a global equivalent method was discussed in case of ignoring the shear deformation of the core. In this way, the reinforced structure could be made equivalence to orthotropic thin plate and stiffness coefficients equations were presented. Secondly, when considering shear deformation of the core, equivalent elastic coefficients of the core compounded by crossing walls and polyurethane elastomers were also given by theoretical derivation. Finally, the equivalent orthotropic modules for the polyurethane core with crossing walls were analyzed by finite element method (FEM) based on equivalent strain energy density. And the results show that the error between theoretical derivation and FEM is less than 10%.
2017, 34(3): 574-581.
doi: 10.13801/j.cnki.fhclxb.20160523.013
Abstract:
Based on a novel micromechanics modeling method-variational asymptotic homogenization theory, a micromechanics model for magnetostrictive composites was established to accurately predict the effective material properties and local distribution of stress and magnetic flux density. Starting from the total magnetic enthalpy of the magnetostrictive composites, the exact solutions of field variables in the magnetic enthalpy were expressed as the sum of mean values and the fluctuation function. According to the principle of minimum potential energy, the micromechanics model was formulated as a constrained stationary problem by taking advantage of the small parameters of the ratio of microscopic scale to macroscopic scale. To handle the microstructures in realistic engineering applications, the new model using the finite element discretization technique was implemented. The numerical example of CoFe2O4/epoxy composites show that the model can accurately predict the effective properties and the local field distribution of magnetostrictive composites, and can be extended to the effective properties and local field analysis of other multiphase composites.
Based on a novel micromechanics modeling method-variational asymptotic homogenization theory, a micromechanics model for magnetostrictive composites was established to accurately predict the effective material properties and local distribution of stress and magnetic flux density. Starting from the total magnetic enthalpy of the magnetostrictive composites, the exact solutions of field variables in the magnetic enthalpy were expressed as the sum of mean values and the fluctuation function. According to the principle of minimum potential energy, the micromechanics model was formulated as a constrained stationary problem by taking advantage of the small parameters of the ratio of microscopic scale to macroscopic scale. To handle the microstructures in realistic engineering applications, the new model using the finite element discretization technique was implemented. The numerical example of CoFe2O4/epoxy composites show that the model can accurately predict the effective properties and the local field distribution of magnetostrictive composites, and can be extended to the effective properties and local field analysis of other multiphase composites.
2017, 34(3): 582-587.
doi: 10.13801/j.cnki.fhclxb.20160612.014
Abstract:
Epoxy tung-maleic anhydride adhesive is an important part of high voltage electrical machine main insulation, and affects the stable and safe operation of electrical machine directly. In order to improve the mechanical and aging property of the epoxy tung-maleic anhydride adhesive, the nano-SiO2/epoxy tung-maleic anhydride adhesive composites with the mass fraction of 1 wt%, 2 wt%, 3 wt% and 4 wt% nano-SiO2 were made respectively. The flexural strength and impact strength, and the breakdown strength before and after thermal aging and electrical aging of the composite were measured. The results indicate that flexural strength of 1 wt% nano-SiO2/epoxy tung-maleic anhydride adhesive composite increases by 24. 79%, and impact strength of 2 wt% nano-SiO2 loading composite increases by 47.11%. Before the aging, the breakdown strength of the composites increases with the increasing of nano-SiO2 loading first, and then decrease. When the nano-SiO2 loading is 2 wt%, the breakdown strength of nano-SiO2/epoxy tung-maleic anhydride adhesive reaches the maximum and increases by 7.3%. After electrical aging as well as at early period of the thermal aging, the breakdown strength of 1 wt% and 2 wt% nano-SiO2 loading composite are higher than that of the unfilled adhesive. But at the end of 28 days thermal aging, the breakdown strength of all the composites and unfilled epoxy tung-maleic anhydride adhesive tend to be same.
Epoxy tung-maleic anhydride adhesive is an important part of high voltage electrical machine main insulation, and affects the stable and safe operation of electrical machine directly. In order to improve the mechanical and aging property of the epoxy tung-maleic anhydride adhesive, the nano-SiO2/epoxy tung-maleic anhydride adhesive composites with the mass fraction of 1 wt%, 2 wt%, 3 wt% and 4 wt% nano-SiO2 were made respectively. The flexural strength and impact strength, and the breakdown strength before and after thermal aging and electrical aging of the composite were measured. The results indicate that flexural strength of 1 wt% nano-SiO2/epoxy tung-maleic anhydride adhesive composite increases by 24. 79%, and impact strength of 2 wt% nano-SiO2 loading composite increases by 47.11%. Before the aging, the breakdown strength of the composites increases with the increasing of nano-SiO2 loading first, and then decrease. When the nano-SiO2 loading is 2 wt%, the breakdown strength of nano-SiO2/epoxy tung-maleic anhydride adhesive reaches the maximum and increases by 7.3%. After electrical aging as well as at early period of the thermal aging, the breakdown strength of 1 wt% and 2 wt% nano-SiO2 loading composite are higher than that of the unfilled adhesive. But at the end of 28 days thermal aging, the breakdown strength of all the composites and unfilled epoxy tung-maleic anhydride adhesive tend to be same.
2017, 34(3): 588-596.
doi: 10.13801/j.cnki.fhclxb.20160523.015
Abstract:
In order to investigate on buckling behavior of some composite cylindrical shells considering multimode imperfections, linear buckling analysis was performed for the perfect cylindrical shell under axial compressed condition to obtain the first fifty buckling modes, defined as mode imperfections. Nonlinear buckling analysis of the cylindrical shell under different mode imperfection was proposed based on the Riks method. Buckling loads calculated using finite element analysis results and empirical method results according to NASA SP-8007 were compared with Bisagni's test results. The results show that the first mode imperfection is not the worst imperfection for composite cylindrical shells under axial compressed condition. Buckling load obtained from the first mode imperfection is much higher than the experimental result. And buckling load obtained from higher mode imperfection agrees well with the experimental result. The decrease of buckling load is influenced by shape and amplitude of imperfection synchronously. The multi-mode effects should be considered on buckling analysis of composite cylindrical shells. Buckling load obtained from NASA is very conservative, which is much lower than the test result. Designing composite cylindrical shells according to NASA always results in heavy structure, material redundancy and poor performance.
In order to investigate on buckling behavior of some composite cylindrical shells considering multimode imperfections, linear buckling analysis was performed for the perfect cylindrical shell under axial compressed condition to obtain the first fifty buckling modes, defined as mode imperfections. Nonlinear buckling analysis of the cylindrical shell under different mode imperfection was proposed based on the Riks method. Buckling loads calculated using finite element analysis results and empirical method results according to NASA SP-8007 were compared with Bisagni's test results. The results show that the first mode imperfection is not the worst imperfection for composite cylindrical shells under axial compressed condition. Buckling load obtained from the first mode imperfection is much higher than the experimental result. And buckling load obtained from higher mode imperfection agrees well with the experimental result. The decrease of buckling load is influenced by shape and amplitude of imperfection synchronously. The multi-mode effects should be considered on buckling analysis of composite cylindrical shells. Buckling load obtained from NASA is very conservative, which is much lower than the test result. Designing composite cylindrical shells according to NASA always results in heavy structure, material redundancy and poor performance.
2017, 34(3): 597-603.
doi: 10.13801/j.cnki.fhclxb.20160523.016
Abstract:
To provide basic comprehension into formation mechanism and spatial distribution of the nano-B4CP(n-B4CP,50nm), as well as the influence of nano-particle distribution on mechanical properties of 6 vol% n-B4CP/2009Al composite. 6 vol% B4C nanoparticles reinforced 2009Al matrix(6 vol% n-B4CP/2009Al) composite was fabricated by efficient 3D mixermulti-stage vacuum hot pressing and hot extrusion method. The results show that, when the ball charge mass ratio is 5:1, B4C nanoparticles can be distributed uniformly on the surface of Al alloy powders after 30 h milling. The B4C nanoparticles of 6 vol% n-B4CP/2009Al composite in hot pressing state segregate at the matrix boundary, which are uniformly distributed after hot extrusion. During hot extrusion process, the chief mechanism of homogenizing B4C nanoparticles is that the plastic flow of alloy matrix impose a shear pressure upon B4C nanoparticles at the matrix boundary and then the cracked B4C nanoparticles aggregates redistributed along the direction of the shear force. After a solution treatment at 495℃ for 1 h,followed by water quenching and artificial aging at 175℃ for 16 h, the hardness of 6 vol% n-B4CP/2009Al composite is 36.4% higher than that of pure 2009Al alloy, and tensile strength and yield strength increase 10.9% and 26.2% respectively. The tensile fracture surface of 6 vol% n-B4CP/2009Al composite reveals a mixing characteristic of ductile and brittle fractures.
To provide basic comprehension into formation mechanism and spatial distribution of the nano-B4CP(n-B4CP,50nm), as well as the influence of nano-particle distribution on mechanical properties of 6 vol% n-B4CP/2009Al composite. 6 vol% B4C nanoparticles reinforced 2009Al matrix(6 vol% n-B4CP/2009Al) composite was fabricated by efficient 3D mixermulti-stage vacuum hot pressing and hot extrusion method. The results show that, when the ball charge mass ratio is 5:1, B4C nanoparticles can be distributed uniformly on the surface of Al alloy powders after 30 h milling. The B4C nanoparticles of 6 vol% n-B4CP/2009Al composite in hot pressing state segregate at the matrix boundary, which are uniformly distributed after hot extrusion. During hot extrusion process, the chief mechanism of homogenizing B4C nanoparticles is that the plastic flow of alloy matrix impose a shear pressure upon B4C nanoparticles at the matrix boundary and then the cracked B4C nanoparticles aggregates redistributed along the direction of the shear force. After a solution treatment at 495℃ for 1 h,followed by water quenching and artificial aging at 175℃ for 16 h, the hardness of 6 vol% n-B4CP/2009Al composite is 36.4% higher than that of pure 2009Al alloy, and tensile strength and yield strength increase 10.9% and 26.2% respectively. The tensile fracture surface of 6 vol% n-B4CP/2009Al composite reveals a mixing characteristic of ductile and brittle fractures.
2017, 34(3): 604-610.
doi: 10.13801/j.cnki.fhclxb.20160926.017
Abstract:
In order to develop new type magnesia refractories, aluminum powder, silicon powder and fused magnesia powder were used as the raw matters, the polytypic Mg-sialon phase forming in the composite material of MgO, Al and Si sintered at 1350℃ and 1550℃ in oxidizing, reducing and nitrogen atmosphere were characterized by XRD, SEM and energy dispersion spectrum (EDS) respectively, and the formation mechanism of polytypic Mg-sialon phase were explained by thermodynamic analysis at the same time. The experiment result shows that after sintering in both oxidizing, reducing or nitrogen atmosphere, Al and Si in sintered composites mainly translate into Al2O3, AlN and SiO2 by gas-solid/liquid reaction, and then react with MgO to form polytypic Mg-sialon phase. The polytypic Mg-sialon phase in-situ synthesized in Mg-sialon/MgO composite of MgO, Al and Si sintered in three different atmospheres all show plate-like shape, and it is mainly forms in the closed pores of the specimen sintered in oxidizing atmosphere, holes left behind by the molten metal in the specimen sintered in reducing atmosphere and whole area of the specimen sintered in nitrogen atmosphere.
In order to develop new type magnesia refractories, aluminum powder, silicon powder and fused magnesia powder were used as the raw matters, the polytypic Mg-sialon phase forming in the composite material of MgO, Al and Si sintered at 1350℃ and 1550℃ in oxidizing, reducing and nitrogen atmosphere were characterized by XRD, SEM and energy dispersion spectrum (EDS) respectively, and the formation mechanism of polytypic Mg-sialon phase were explained by thermodynamic analysis at the same time. The experiment result shows that after sintering in both oxidizing, reducing or nitrogen atmosphere, Al and Si in sintered composites mainly translate into Al2O3, AlN and SiO2 by gas-solid/liquid reaction, and then react with MgO to form polytypic Mg-sialon phase. The polytypic Mg-sialon phase in-situ synthesized in Mg-sialon/MgO composite of MgO, Al and Si sintered in three different atmospheres all show plate-like shape, and it is mainly forms in the closed pores of the specimen sintered in oxidizing atmosphere, holes left behind by the molten metal in the specimen sintered in reducing atmosphere and whole area of the specimen sintered in nitrogen atmosphere.
2017, 34(3): 611-618.
doi: 10.13801/j.cnki.fhclxb.20161123.018
Abstract:
The SiCP/AZ91 composite was fabricated by stir-casting and then processed by equal channel angular pressing (ECAP) at different temperature successfully. No obvious SiCP clusters and porosities are observed in the cast SiCP/AZ91 composite. Most SiCP particles are segregated at a microscopic scale near the grain boundary regions, which is typical "necklace-type" particle distribution for SiCP/AZ91 composite fabricated by stir casting. With increasing of ECAP passes, the SiCP distribution is improved and no obvious particle broken is discovered in SiC/AZ91 after ECAP. The grains of the AZ91 matrix are refined gradually due to the dynamic recrystallization. The matrix grain refinement and the improved particle distribution result in the increase of tensile yield strength and ultimate strength of the composite during ECAP processing.
The SiCP/AZ91 composite was fabricated by stir-casting and then processed by equal channel angular pressing (ECAP) at different temperature successfully. No obvious SiCP clusters and porosities are observed in the cast SiCP/AZ91 composite. Most SiCP particles are segregated at a microscopic scale near the grain boundary regions, which is typical "necklace-type" particle distribution for SiCP/AZ91 composite fabricated by stir casting. With increasing of ECAP passes, the SiCP distribution is improved and no obvious particle broken is discovered in SiC/AZ91 after ECAP. The grains of the AZ91 matrix are refined gradually due to the dynamic recrystallization. The matrix grain refinement and the improved particle distribution result in the increase of tensile yield strength and ultimate strength of the composite during ECAP processing.
2017, 34(3): 619-624.
doi: 10.13801/j.cnki.fhclxb.20160511.019
Abstract:
Nano diamond and boric anhydride were melted together at high temperature and then was mixed with alumina sol solution. Different proportions of hexogeon powder mixed homogeneously to precursor powder were made into blasting charges. Cartridges were detonated and products were collected. XRD and transmission electron microscopy with selected area electron diffraction were used to characterize the obtained detonation products. And BKW calculation program was used to operate special explosive detonation parameters contained Al and B element.The results show that nano diamond-Al2O3 full-package structures are found. The polar material compatibility and good dispersion stability are connected to such nano particle. The product generation mechanism is explored. The chemical bonds are broken by temperature and pressure produced by detonation reaction. The droplet is formed of radical B2O3-nano diamond, Al2O3 after collision. Al2O3 is made into a ball at high temperature. And radical B2O3-nano diamond is absorbed. More perfect encapsulation structure and bigger nano diamond is produced by more hexogeon.
Nano diamond and boric anhydride were melted together at high temperature and then was mixed with alumina sol solution. Different proportions of hexogeon powder mixed homogeneously to precursor powder were made into blasting charges. Cartridges were detonated and products were collected. XRD and transmission electron microscopy with selected area electron diffraction were used to characterize the obtained detonation products. And BKW calculation program was used to operate special explosive detonation parameters contained Al and B element.The results show that nano diamond-Al2O3 full-package structures are found. The polar material compatibility and good dispersion stability are connected to such nano particle. The product generation mechanism is explored. The chemical bonds are broken by temperature and pressure produced by detonation reaction. The droplet is formed of radical B2O3-nano diamond, Al2O3 after collision. Al2O3 is made into a ball at high temperature. And radical B2O3-nano diamond is absorbed. More perfect encapsulation structure and bigger nano diamond is produced by more hexogeon.
2017, 34(3): 625-631.
doi: 10.13801/j.cnki.fhclxb.20160612.020
Abstract:
To improve the thermal stability and electrolyte wettability of polyolefin-based separators, a high performance organic-inorganic composite separator was prepared by a phase inversion process using microporous zeolite nano-particles and polyvinylidene fluoride (PVDF). The results show that compared with the polyolefin-based separator(PE), the zeolite/PVDF composite separator exhibits well-developed microstructure, superior thermal resistance and excellent liquid electrolyte wettability, for example the porosity of the present separator is over 70% which is about one time higher than that of PE separator, and the zeolite/PVDF composite separator exhibits exce-llent thermal stabilitywith area shrinkage of 5% after the heat treatment at 160℃ for 0.5 h, while PE separator and PVDF separator show 100% and 50% thermal shrinkage under the same condition respectively. Moreover, the electrolyte contact angle of zeolite/PVDF composite separator is about 7.4°, while those of PE separator and PVDF separator are about 42.5° and 31.7°. Based on the above advantages, zeolite/PVDF composite separator exhibits better electrochemical performances, such as the C-rate discharge capability and cycling performance, as compared to the commercialized PE separator.
To improve the thermal stability and electrolyte wettability of polyolefin-based separators, a high performance organic-inorganic composite separator was prepared by a phase inversion process using microporous zeolite nano-particles and polyvinylidene fluoride (PVDF). The results show that compared with the polyolefin-based separator(PE), the zeolite/PVDF composite separator exhibits well-developed microstructure, superior thermal resistance and excellent liquid electrolyte wettability, for example the porosity of the present separator is over 70% which is about one time higher than that of PE separator, and the zeolite/PVDF composite separator exhibits exce-llent thermal stabilitywith area shrinkage of 5% after the heat treatment at 160℃ for 0.5 h, while PE separator and PVDF separator show 100% and 50% thermal shrinkage under the same condition respectively. Moreover, the electrolyte contact angle of zeolite/PVDF composite separator is about 7.4°, while those of PE separator and PVDF separator are about 42.5° and 31.7°. Based on the above advantages, zeolite/PVDF composite separator exhibits better electrochemical performances, such as the C-rate discharge capability and cycling performance, as compared to the commercialized PE separator.
2017, 34(3): 632-637.
doi: 10.13801/j.cnki.fhclxb.20160530.021
Abstract:
CoFe2O4 powders of spinel structure and BaTiO3 powders of perovskite structure were prepared using solid phase synthesis. Then the powders were mixed in the molar ratio of 2:8. The different sintering aids were added. The effect of additive on composition microstructure, dielectric properties, ferroelectric properties and magnetic properties of CoFe2O4/BaTiO3 multiphase magnetoelectric material were studied. The results show that it is difficult to achieve the purpose of sintering densification when only Bi2O3 is added; when sintering aids containing CaCO3-SiO2, the sintering performance of CoFe2O4/BaTiO3 multiphase magnetoelectric material is improved. At the same sintering temperature, the density of CoFe2O4/BaTiO3 multiphase magnetoelectric material is improved, and the dielectric properties, ferroelectric and magnetic properties are optimized for a certain degree.
CoFe2O4 powders of spinel structure and BaTiO3 powders of perovskite structure were prepared using solid phase synthesis. Then the powders were mixed in the molar ratio of 2:8. The different sintering aids were added. The effect of additive on composition microstructure, dielectric properties, ferroelectric properties and magnetic properties of CoFe2O4/BaTiO3 multiphase magnetoelectric material were studied. The results show that it is difficult to achieve the purpose of sintering densification when only Bi2O3 is added; when sintering aids containing CaCO3-SiO2, the sintering performance of CoFe2O4/BaTiO3 multiphase magnetoelectric material is improved. At the same sintering temperature, the density of CoFe2O4/BaTiO3 multiphase magnetoelectric material is improved, and the dielectric properties, ferroelectric and magnetic properties are optimized for a certain degree.
2017, 34(3): 638-645.
doi: 10.13801/j.cnki.fhclxb.20160523.022
Abstract:
The Silicate glasses in TiO2/SiO2-Al2O3-MgO system doping with 0-1.8 wt% TiO2 were prepared by the conventional melt quenching technique, and the effects of TiO2 on the density, bending strength, compressive strength, compression modulus and structural stability were investigated. When the content of TiO2 is less than 1.5 wt% (mass fraction), the density, bending strength, compressive strength and compression modulus increase with the increasing of TiO2 content, and the optical band gap decreases with the TiO2 content increasing. As the content of TiO2 is more than 1.5 wt%, the density, bending strength, compressive strength and compression modulus decrease with the increasing of TiO2 content, and the optical band gap increases with the increasing of TiO2 content. When the content of TiO2 is 1.5 wt%, the mechanical properties of the TiO2/SiO2-Al2O3-MgO system is excellent, and the bending strength, compressive strength, compression modulus and optical band gap of the glasses is 110.36 MPa, 240.18 MPa, 115.03 GPa and 3.75 eV, respectively. The addition of TiO2 reduces the numbers of the non-bridging oxygen in the glass network structure, increasing the structural stability of the investigated glasses. So the network structure of the isolated island is rejoined, which significantly improve the mechanical properties of the glass. However, excessive TiO2 force its structure of the bridge oxygen bond to generate non-bridging oxygen, which significantly reduces the structural stability and mechanical properties of the investigated glasses.
The Silicate glasses in TiO2/SiO2-Al2O3-MgO system doping with 0-1.8 wt% TiO2 were prepared by the conventional melt quenching technique, and the effects of TiO2 on the density, bending strength, compressive strength, compression modulus and structural stability were investigated. When the content of TiO2 is less than 1.5 wt% (mass fraction), the density, bending strength, compressive strength and compression modulus increase with the increasing of TiO2 content, and the optical band gap decreases with the TiO2 content increasing. As the content of TiO2 is more than 1.5 wt%, the density, bending strength, compressive strength and compression modulus decrease with the increasing of TiO2 content, and the optical band gap increases with the increasing of TiO2 content. When the content of TiO2 is 1.5 wt%, the mechanical properties of the TiO2/SiO2-Al2O3-MgO system is excellent, and the bending strength, compressive strength, compression modulus and optical band gap of the glasses is 110.36 MPa, 240.18 MPa, 115.03 GPa and 3.75 eV, respectively. The addition of TiO2 reduces the numbers of the non-bridging oxygen in the glass network structure, increasing the structural stability of the investigated glasses. So the network structure of the isolated island is rejoined, which significantly improve the mechanical properties of the glass. However, excessive TiO2 force its structure of the bridge oxygen bond to generate non-bridging oxygen, which significantly reduces the structural stability and mechanical properties of the investigated glasses.
2017, 34(3): 646-652.
doi: 10.13801/j.cnki.fhclxb.20160607.023
Abstract:
The waste walnut shell was used to prepare biomass porous carbon (PC). Capric acid (CA) was encapsulated into the PC by vacuum absorption. And the CA-PC composites were prepared. The CA-PC/Di-Gy multi-functional composites were made by CA-PC composites, diatomite (Di) and gypsum (Gy). The thermal property, heat property and moisture property of the CA-PC/Di-Gy multi-functional composites were tested respectively. The prepared samples were characterized by using BET, FTIR, SEM and DSC. The results show that the PC made by waste walnut shell has high developed pore structure which not only can package CA but also can adsorb formaldehyde. The temperature-humidity control property and adsorption rate to formaldehyde of the CA-PC/Di-Gy multi-functional composites are good. The constant temperature platform is about 32℃. The equilibrium moisture content is 0.0859-0.2310 g/g during the 40%-60% reality humidity. And the adsorption effect is close to 40% after 4 h of formaldehyde.
The waste walnut shell was used to prepare biomass porous carbon (PC). Capric acid (CA) was encapsulated into the PC by vacuum absorption. And the CA-PC composites were prepared. The CA-PC/Di-Gy multi-functional composites were made by CA-PC composites, diatomite (Di) and gypsum (Gy). The thermal property, heat property and moisture property of the CA-PC/Di-Gy multi-functional composites were tested respectively. The prepared samples were characterized by using BET, FTIR, SEM and DSC. The results show that the PC made by waste walnut shell has high developed pore structure which not only can package CA but also can adsorb formaldehyde. The temperature-humidity control property and adsorption rate to formaldehyde of the CA-PC/Di-Gy multi-functional composites are good. The constant temperature platform is about 32℃. The equilibrium moisture content is 0.0859-0.2310 g/g during the 40%-60% reality humidity. And the adsorption effect is close to 40% after 4 h of formaldehyde.
2017, 34(3): 653-660.
doi: 10.13801/j.cnki.fhclxb.20160607.024
Abstract:
In this paper, the hydration process of Portland cement and CNTs reinforced samples at the early age was characterized by FTIR spectroscopy. The rustles show that FTIR is a simple and rapid research method in operation, which can reflect the basic variation in the primary cement hydration products. With the proceeding of hydration reaction, the peak value corresponding to Si-O vibrations in FTIR spectrum shifts from low wavenumbers to high wavenumbers, which not only reflects the polymerization process of silicon-oxygen tetrahedrons in the C-S-H gel, but also the hydration reaction speed of cement paste at this stage. This viewpoint was confirmed by the experiment for the samples with added superplasticizer. The shifting characteristics of the absorption peaks in the range 800-1 025 cm-1 for the samples at the ages of 8-12 h were comprehensively investigated in this study. The research results show that the shifting speed of the characteristic peak for the blank sample is exactly the same as that for the sample reinforced with CNTs. Therefore, addition of CNTs materials into Portland cement doesn't influence the hydration reaction at the early age. This conclusion is verified by the calorimetry test for hydration temperature.
In this paper, the hydration process of Portland cement and CNTs reinforced samples at the early age was characterized by FTIR spectroscopy. The rustles show that FTIR is a simple and rapid research method in operation, which can reflect the basic variation in the primary cement hydration products. With the proceeding of hydration reaction, the peak value corresponding to Si-O vibrations in FTIR spectrum shifts from low wavenumbers to high wavenumbers, which not only reflects the polymerization process of silicon-oxygen tetrahedrons in the C-S-H gel, but also the hydration reaction speed of cement paste at this stage. This viewpoint was confirmed by the experiment for the samples with added superplasticizer. The shifting characteristics of the absorption peaks in the range 800-1 025 cm-1 for the samples at the ages of 8-12 h were comprehensively investigated in this study. The research results show that the shifting speed of the characteristic peak for the blank sample is exactly the same as that for the sample reinforced with CNTs. Therefore, addition of CNTs materials into Portland cement doesn't influence the hydration reaction at the early age. This conclusion is verified by the calorimetry test for hydration temperature.
2017, 34(3): 661-667.
doi: 10.13801/j.cnki.fhclxb.20160523.025
Abstract:
Melamine(M)-formaldehyde(F)@n-octadecane(OD) micro-encapsulated phase change composites with OD core and M-F polymer shell were synthesized by nonionic/anionic composite emulsifier via in-situ polymerization. The chemical structure, particle size distribution, micro-morphology and thermal properties of the M-F@OD micro-encapsulated phase change composites were characterized by FTIR, SEM, DSC and laser particle analyzer. The results show that the combination and dosage of different emulsifier produce a significant impact on the morphology and properties of the M-F@OD micro-encapsulated phase change composites. As the anionic/nonionic composite emulsifier is used, the phenomenon of agglomeration of the M-F@OD phase change composites is improved, the particle size distribution of the M-F@OD phase change composites is more uniform, the particle size is further refined which is 0.1-1 μm, providing a high energy storage capacity of 70.86 J/g.
Melamine(M)-formaldehyde(F)@n-octadecane(OD) micro-encapsulated phase change composites with OD core and M-F polymer shell were synthesized by nonionic/anionic composite emulsifier via in-situ polymerization. The chemical structure, particle size distribution, micro-morphology and thermal properties of the M-F@OD micro-encapsulated phase change composites were characterized by FTIR, SEM, DSC and laser particle analyzer. The results show that the combination and dosage of different emulsifier produce a significant impact on the morphology and properties of the M-F@OD micro-encapsulated phase change composites. As the anionic/nonionic composite emulsifier is used, the phenomenon of agglomeration of the M-F@OD phase change composites is improved, the particle size distribution of the M-F@OD phase change composites is more uniform, the particle size is further refined which is 0.1-1 μm, providing a high energy storage capacity of 70.86 J/g.
2017, 34(3): 668-674.
doi: 10.13801/j.cnki.fhclxb.20160418.026
Abstract:
Carbon fiber was considered to be a two-phase composite composed of crystallites and amorphous components. The Mori-Tanaka method was used to investigate the relationship between the microstructure of carbon fibers and the tensile modulus of carbon fibers. In order to follow the dependence of the tensile modulus on microstructure, four types of high modulus carbon fibers M35JB, M40JB, M46JB and M55JB were prepared. The aspect ratio of crystallites was measured by XRD and the degree of graphitization was obtained by Raman spectroscopy. Factors that affect the tensile modulus included the aspect ratio, volume fraction and orientation degree of crystallites. The volume fraction of crystallites was obtained by calculating the micromechanical model. It is found that the higher the degree of graphitization is, the higher the volume fraction of crystallites is. Some relationships are concluded that the tensile modulus increases with the increase of the volume fraction, aspect ratio and orientation degree of crystallites. The three factors are compared. The volume fraction and orientation degree of crystallites have a greater effect on tensile modulus than the aspect ratio of crystallites, and it is only when the orientation degree of crystallites approaches 100%, the effect of the orientation degree of crystallites on tensile modulus may be surpassed by the aspect ratio of crystallites. Comparing the volume fraction of crystallites with the orientation degree of crystallites, it can be found that the orientation degree of crystallites has a greater effect than the volume fraction of crystallites in the initial, but with the increase of the two factors, the effect of the orientation degree of crystallites on tensile modulus is surpassed by the volume fractions of crystallites.
Carbon fiber was considered to be a two-phase composite composed of crystallites and amorphous components. The Mori-Tanaka method was used to investigate the relationship between the microstructure of carbon fibers and the tensile modulus of carbon fibers. In order to follow the dependence of the tensile modulus on microstructure, four types of high modulus carbon fibers M35JB, M40JB, M46JB and M55JB were prepared. The aspect ratio of crystallites was measured by XRD and the degree of graphitization was obtained by Raman spectroscopy. Factors that affect the tensile modulus included the aspect ratio, volume fraction and orientation degree of crystallites. The volume fraction of crystallites was obtained by calculating the micromechanical model. It is found that the higher the degree of graphitization is, the higher the volume fraction of crystallites is. Some relationships are concluded that the tensile modulus increases with the increase of the volume fraction, aspect ratio and orientation degree of crystallites. The three factors are compared. The volume fraction and orientation degree of crystallites have a greater effect on tensile modulus than the aspect ratio of crystallites, and it is only when the orientation degree of crystallites approaches 100%, the effect of the orientation degree of crystallites on tensile modulus may be surpassed by the aspect ratio of crystallites. Comparing the volume fraction of crystallites with the orientation degree of crystallites, it can be found that the orientation degree of crystallites has a greater effect than the volume fraction of crystallites in the initial, but with the increase of the two factors, the effect of the orientation degree of crystallites on tensile modulus is surpassed by the volume fractions of crystallites.
2017, 34(3): 675-683.
doi: 10.13801/j.cnki.fhclxb.20160531.027
Abstract:
In order to investigate the strain rate and temperature effect on the flexural mechanical properties of alkali-resistant glass fabric reinforced cement matrix (FRCM) composite, the FRCM composite specimens were tested under quasi-static (3.33×10-5 s-1) loading in 3-point bending set-up using a MTS load frame at room temperature (25℃), and under dynamic loading in the same 3-point bending set-up at different strain rates (4, 8, 12, 16 and 18 s-1) and distinct temperatures (-50, 0, 25, 50 and 100℃) utilizing an INSTRON drop-tower impact system. The same fixture was used in quasi-static and dynamic flexural tests. The effect of the number of reinforcing fabric layers on their flexural mechanical properties was also taken into consideration. The experimental results show that, at room temperature, flexural strength increases with increasing strain rate, but flexural ultimate strain and toughness firstly decrease and then increase with increasing strain rate, and flexural modulus firstly increases and then decreases with increasing strain rate. At the same flexural strain rate of 12 s-1, flexural strength, flexural modulus and toughness decrease with increasing temperature, and ultimate strain does not change significantly. When alkali-resistant glass fabric with six layers is used in the composite specimens, the reinforcing effect is more significant. The strain rate, temperature and the number of reinforcing fabric layers can significantly affect the flexural performance of specimens.
In order to investigate the strain rate and temperature effect on the flexural mechanical properties of alkali-resistant glass fabric reinforced cement matrix (FRCM) composite, the FRCM composite specimens were tested under quasi-static (3.33×10-5 s-1) loading in 3-point bending set-up using a MTS load frame at room temperature (25℃), and under dynamic loading in the same 3-point bending set-up at different strain rates (4, 8, 12, 16 and 18 s-1) and distinct temperatures (-50, 0, 25, 50 and 100℃) utilizing an INSTRON drop-tower impact system. The same fixture was used in quasi-static and dynamic flexural tests. The effect of the number of reinforcing fabric layers on their flexural mechanical properties was also taken into consideration. The experimental results show that, at room temperature, flexural strength increases with increasing strain rate, but flexural ultimate strain and toughness firstly decrease and then increase with increasing strain rate, and flexural modulus firstly increases and then decreases with increasing strain rate. At the same flexural strain rate of 12 s-1, flexural strength, flexural modulus and toughness decrease with increasing temperature, and ultimate strain does not change significantly. When alkali-resistant glass fabric with six layers is used in the composite specimens, the reinforcing effect is more significant. The strain rate, temperature and the number of reinforcing fabric layers can significantly affect the flexural performance of specimens.
2017, 34(3): 684-690.
doi: 10.13801/j.cnki.fhclxb.20160523.028
Abstract:
Natural rubber (NR) reinforced with pitch-based chopped carbon fiber (PCF) modified by nitric acid (HNO3) or blending with carbon black (CB) or Silica was studied. The effects of the surface modification and blending on the surface morphology and microstructure of PCF and mechanical properties of NR matrix composites were investigated, and the mechanism of interfacial interaction between the filler and the matrix was analyzed. The results show that the surface roughness and O/C ratio of PCF are improved evidently, while graphitization degree decrease somewhat by HNO3 treatment. PCF has no reinforcing effect on NR when used alone. However, the tensile strength of NR improves martially by blending PCF with CB or Silica, which enhance from about 3 MPa to 18.6 MPa and 23.7 MPa, respectively, and to 24.5 MPa and 24.7 MPa after modification. Compared with of CB/NR vulcanizates, the tensile strength of PCF-CB/NR vulcanizates decreases slightly, but it enhances 25.6% for PCF-CB/NR vulcanizates. The tensile strength of PCF-Silica/NR where PCF modified or not is a little lower modifieated than that of Silica/NR vulcanizates. Combined with mechanical properties, 50% modulus of different reinforcing system and SEM of fracture section, it can be deduced that the improved interfacial interaction in PCF-CB and NR could be mainly attributed to adsorption theory and a subtle mixture of mechanical interlocking and adsorption theory before and after modification of PCF, but nearly hydrogen bonding in PCF-Silica and NR interface, whether modified or not.
Natural rubber (NR) reinforced with pitch-based chopped carbon fiber (PCF) modified by nitric acid (HNO3) or blending with carbon black (CB) or Silica was studied. The effects of the surface modification and blending on the surface morphology and microstructure of PCF and mechanical properties of NR matrix composites were investigated, and the mechanism of interfacial interaction between the filler and the matrix was analyzed. The results show that the surface roughness and O/C ratio of PCF are improved evidently, while graphitization degree decrease somewhat by HNO3 treatment. PCF has no reinforcing effect on NR when used alone. However, the tensile strength of NR improves martially by blending PCF with CB or Silica, which enhance from about 3 MPa to 18.6 MPa and 23.7 MPa, respectively, and to 24.5 MPa and 24.7 MPa after modification. Compared with of CB/NR vulcanizates, the tensile strength of PCF-CB/NR vulcanizates decreases slightly, but it enhances 25.6% for PCF-CB/NR vulcanizates. The tensile strength of PCF-Silica/NR where PCF modified or not is a little lower modifieated than that of Silica/NR vulcanizates. Combined with mechanical properties, 50% modulus of different reinforcing system and SEM of fracture section, it can be deduced that the improved interfacial interaction in PCF-CB and NR could be mainly attributed to adsorption theory and a subtle mixture of mechanical interlocking and adsorption theory before and after modification of PCF, but nearly hydrogen bonding in PCF-Silica and NR interface, whether modified or not.
2017, 34(3): 691-697.
doi: 10.13801/j.cnki.fhclxb.20160616.029
Abstract:
Silt and carbon were used to prepare conductive geo-material, the testing method characterized by distributed electrodes on surface of the soil sample was adopted to measure the distribution of internal resistance increment along the direction of compression. Test results indicate that the resistance variation rate induced from the initiation of the internal fissures can represent the stress state synchronized and sensitive. According to the measurement of resistance variation rate between different electrodes, the propagation of fissures in different zones can be revealed. This study shows that the resistance is sensitive to the extension of fissures. The testing method with distributed electrodes can capture and reflect the evolution of fissures in different zones of soil sample under uniaxial compression. And it has the preliminary capacity to self-test.
Silt and carbon were used to prepare conductive geo-material, the testing method characterized by distributed electrodes on surface of the soil sample was adopted to measure the distribution of internal resistance increment along the direction of compression. Test results indicate that the resistance variation rate induced from the initiation of the internal fissures can represent the stress state synchronized and sensitive. According to the measurement of resistance variation rate between different electrodes, the propagation of fissures in different zones can be revealed. This study shows that the resistance is sensitive to the extension of fissures. The testing method with distributed electrodes can capture and reflect the evolution of fissures in different zones of soil sample under uniaxial compression. And it has the preliminary capacity to self-test.
2017, 34(3): 698-698.
Abstract:
