2018 Vol. 35, No. 5
2018, 35(5): 1033-1049.
doi: 10.13801/j.cnki.fhclxb.20180328.003
Abstract:
Carbon nanotubes(CNTs) are drawing widespread attention due to the unique structure and excellent properties, such as the mechanical property and the electrical property. It will significantly improve the cement-based composites' properties when adding CNTs into composites. The CNTs' basic properties and dispersion methods, and elucidated the properties of cement-based composites recombining CNTs, including the mechanical property, the deformation property, the durability property, the thermal conductivities, electrical conductivities and microwave absorbing properties were briefly introduced. The problems existing in present research were also summarized, and some proposes for future study were given.
Carbon nanotubes(CNTs) are drawing widespread attention due to the unique structure and excellent properties, such as the mechanical property and the electrical property. It will significantly improve the cement-based composites' properties when adding CNTs into composites. The CNTs' basic properties and dispersion methods, and elucidated the properties of cement-based composites recombining CNTs, including the mechanical property, the deformation property, the durability property, the thermal conductivities, electrical conductivities and microwave absorbing properties were briefly introduced. The problems existing in present research were also summarized, and some proposes for future study were given.
2018, 35(5): 1050-1058.
doi: 10.13801/j.cnki.fhclxb.20170630.001
Abstract:
A series of nano SiO2-Al2O3/polyimide(SiO2-Al2O3/PI) of five layer structure corona resistant film Am An PAn Am were prepared by dipping method, the middle layer (P) was pure PI film, the outer layer (Am) and the secondary layer (An) were nano SiO2-Al2O3/PI composite film doped with different SiO2-Al2O3 mass fraction. The microstructure, dielectric properties and mechanical properties of five layer nano SiO2-Al2O3/PI composite film were characterized by TEM, FTIR, broadband dielectric spectrometer, conduction current tester, corona resistance tester, dielectric strength tester and tensile test machine. The results show that the organic/inorganic composite structure is formed in the doped layer of five layer nano SiO2-Al2O3/PI composite film. The protection of SiO2-Al2O3 nanoparticles is the main factor affecting the corona resistance of five layer nano SiO2-Al2O3/PI composite film, and the corona resistant life of five layer nano SiO2-Al2O3/PI composite film A32A16PA16A32 is the most, which is 23.4 h. The amount of doping in the outer layer has a great influence on the dielectric strength of the five layer composite, the dielectric strength of the composite film A20A28PA28A20 is the largest, which is 302.3 kV/mm. By designing composite structure of five layer film, the mechanical properties of the five layer nano SiO2-Al2O3/PI composite film can be improved as well as the corona resistant life and dielectric strength of the material.
A series of nano SiO2-Al2O3/polyimide(SiO2-Al2O3/PI) of five layer structure corona resistant film Am An PAn Am were prepared by dipping method, the middle layer (P) was pure PI film, the outer layer (Am) and the secondary layer (An) were nano SiO2-Al2O3/PI composite film doped with different SiO2-Al2O3 mass fraction. The microstructure, dielectric properties and mechanical properties of five layer nano SiO2-Al2O3/PI composite film were characterized by TEM, FTIR, broadband dielectric spectrometer, conduction current tester, corona resistance tester, dielectric strength tester and tensile test machine. The results show that the organic/inorganic composite structure is formed in the doped layer of five layer nano SiO2-Al2O3/PI composite film. The protection of SiO2-Al2O3 nanoparticles is the main factor affecting the corona resistance of five layer nano SiO2-Al2O3/PI composite film, and the corona resistant life of five layer nano SiO2-Al2O3/PI composite film A32A16PA16A32 is the most, which is 23.4 h. The amount of doping in the outer layer has a great influence on the dielectric strength of the five layer composite, the dielectric strength of the composite film A20A28PA28A20 is the largest, which is 302.3 kV/mm. By designing composite structure of five layer film, the mechanical properties of the five layer nano SiO2-Al2O3/PI composite film can be improved as well as the corona resistant life and dielectric strength of the material.
2018, 35(5): 1059-1065.
doi: 10.13801/j.cnki.fhclxb.20170926.001
Abstract:
Polypyrrole (PPy) was synthesized by chemical oxidation methods in the presence of toluene sulfonate (TSNa), dodecyl sulfonic acid sodium salt (DSNa), dodecyl-benzene sulfonic acid sodium salt (DBSNa) and di-(2-ethylhexyl) sulfosuccinate sodium salt (DEHS), and then PPy was mixed with polyvinyl alcohol (PVA). PVA-PPy composite nano fibers were prepared via electrospinning. The microstructure, thermal stability and conductivity properties were investigated using SEM, TGA and four-probe tester. The results show that dopants, PPy preparation technology and polymer additives have a great influence on the electrical properties of PPy. The conductivity of nanofibers is much higher than the obtained PVA-PPy films and PPy powders with the same dopant. The conductivity of DEHS doped PVA-PPyPVA-PPy nanofibers is highest among all nanofibers, which reaches to 26.64 S/cm.
Polypyrrole (PPy) was synthesized by chemical oxidation methods in the presence of toluene sulfonate (TSNa), dodecyl sulfonic acid sodium salt (DSNa), dodecyl-benzene sulfonic acid sodium salt (DBSNa) and di-(2-ethylhexyl) sulfosuccinate sodium salt (DEHS), and then PPy was mixed with polyvinyl alcohol (PVA). PVA-PPy composite nano fibers were prepared via electrospinning. The microstructure, thermal stability and conductivity properties were investigated using SEM, TGA and four-probe tester. The results show that dopants, PPy preparation technology and polymer additives have a great influence on the electrical properties of PPy. The conductivity of nanofibers is much higher than the obtained PVA-PPy films and PPy powders with the same dopant. The conductivity of DEHS doped PVA-PPyPVA-PPy nanofibers is highest among all nanofibers, which reaches to 26.64 S/cm.
2018, 35(5): 1066-1072.
doi: 10.13801/j.cnki.fhclxb.20170802.003
Abstract:
In order to prepare a light mass and efficient sound insulation composite, the nitrile rubber(NBR) and polyvinyl chloride(PVC)were blended as the main ingredients and the high-density metal particles (HMP)/NBR-PVC microporous damping composite were prepared by one step molding foaming process. The effect of rubber-plastic mass ratio on the cell structure, damping performance and sound insulation performance of composite materials were studied by SEM, dynamic thermomechanical analysis and the impedance tube measurement. The sound insulation mechanism of HMP/NBR-PVC microporous damping composite was further analyzed. The results show that the presence of microporous structure increases the sound energy attenuation during the propagation inside the composite and improves the sound insulation performance of microporous composite material. The HMP/NBR-PVC microporous damping composite with the NBR and PVC mass ratio of 50:50 displays good cell structure, mechanical properties and damping properties. Its sound insulation index is up to 28.1 dB. The rubber-plastic microporous damping composite shows the advantages such as light mass, soft and easy to process. It has guidance for the development and application of new type sound insulation materials.
In order to prepare a light mass and efficient sound insulation composite, the nitrile rubber(NBR) and polyvinyl chloride(PVC)were blended as the main ingredients and the high-density metal particles (HMP)/NBR-PVC microporous damping composite were prepared by one step molding foaming process. The effect of rubber-plastic mass ratio on the cell structure, damping performance and sound insulation performance of composite materials were studied by SEM, dynamic thermomechanical analysis and the impedance tube measurement. The sound insulation mechanism of HMP/NBR-PVC microporous damping composite was further analyzed. The results show that the presence of microporous structure increases the sound energy attenuation during the propagation inside the composite and improves the sound insulation performance of microporous composite material. The HMP/NBR-PVC microporous damping composite with the NBR and PVC mass ratio of 50:50 displays good cell structure, mechanical properties and damping properties. Its sound insulation index is up to 28.1 dB. The rubber-plastic microporous damping composite shows the advantages such as light mass, soft and easy to process. It has guidance for the development and application of new type sound insulation materials.
2018, 35(5): 1073-1079.
doi: 10.13801/j.cnki.fhclxb.20170713.004
Abstract:
Hexagonal boron nitride (h-BN) was exfoliated by ball-milling method with assistance of melamine. The thicknesses, morphologies and structures of as-prepared melamine-functionalized boron nitride nanoflakes (f-BNNS) were characterized. By investigating the f-BNNS-filled polyvinyl alcohol (PVA) composites, the effects of exfoliation of h-BN and f-BNNS on mechanical properties of composites were studied. The mechanism of interface interaction between f-BNNS and PVA matrix was also analyzed. The results show that most of the f-BNNS exhibit regular rounded flake-liked shape with diameters and thicknesses concentrated on the ranges of 1-3 nm and 150-400 nm, respectively. Comparing with h-BN-filled h-BN/PVA composites, f-BNNS can be well dispersed in PVA matrix. In mean time, the yield strength and elastic modulus of f-BNNS/PVA composites are both improved. When the mass fractions of f-BNNS achieves at 5wt%, the yield strength and elastic modulus f-BNNS/PVA composite films are 175.2 MPa and 4.52 GPa, which are 45.3% and 53.7% higher than that of neat PVA, respectively. From the molecular structures of PVA and f-BNNS and the SEM images of fracture surfaces of f-BNNS/PVA composites, the hydrogen-bonding interaction between the amino groups of f-BNNS and the hydroxyl groups of PVA chains effectively enhances the interfacial interaction between f-BNNS and PVA matrix.
Hexagonal boron nitride (h-BN) was exfoliated by ball-milling method with assistance of melamine. The thicknesses, morphologies and structures of as-prepared melamine-functionalized boron nitride nanoflakes (f-BNNS) were characterized. By investigating the f-BNNS-filled polyvinyl alcohol (PVA) composites, the effects of exfoliation of h-BN and f-BNNS on mechanical properties of composites were studied. The mechanism of interface interaction between f-BNNS and PVA matrix was also analyzed. The results show that most of the f-BNNS exhibit regular rounded flake-liked shape with diameters and thicknesses concentrated on the ranges of 1-3 nm and 150-400 nm, respectively. Comparing with h-BN-filled h-BN/PVA composites, f-BNNS can be well dispersed in PVA matrix. In mean time, the yield strength and elastic modulus of f-BNNS/PVA composites are both improved. When the mass fractions of f-BNNS achieves at 5wt%, the yield strength and elastic modulus f-BNNS/PVA composite films are 175.2 MPa and 4.52 GPa, which are 45.3% and 53.7% higher than that of neat PVA, respectively. From the molecular structures of PVA and f-BNNS and the SEM images of fracture surfaces of f-BNNS/PVA composites, the hydrogen-bonding interaction between the amino groups of f-BNNS and the hydroxyl groups of PVA chains effectively enhances the interfacial interaction between f-BNNS and PVA matrix.
2018, 35(5): 1080-1086.
doi: 10.13801/j.cnki.fhclxb.20170712.002
Abstract:
The continuous glass fiber reinforced polypropylene (GF/PP) prepreg was prepared by melt impregnation method. The rheological measurements show that PP behaves Carreau fluid characteristics. Based on the Darcy's law, an impregnation model of Carreau fluid impregnating continuous GF bundle was proposed, taking the structural parameters, material properties and process parameters into account. The impregnation model was validated after experiments under different impregnation temperatures and pulling speeds, and the experimental results agree with the theoretical values. The impregnation procedure was analyzed by utilizing the model, and the results show that the impregnation degree can be raised significantly through increasing the dipping rolls number and radius, reducing the spacing between the rollers, and increasing the impregnation temperature.
The continuous glass fiber reinforced polypropylene (GF/PP) prepreg was prepared by melt impregnation method. The rheological measurements show that PP behaves Carreau fluid characteristics. Based on the Darcy's law, an impregnation model of Carreau fluid impregnating continuous GF bundle was proposed, taking the structural parameters, material properties and process parameters into account. The impregnation model was validated after experiments under different impregnation temperatures and pulling speeds, and the experimental results agree with the theoretical values. The impregnation procedure was analyzed by utilizing the model, and the results show that the impregnation degree can be raised significantly through increasing the dipping rolls number and radius, reducing the spacing between the rollers, and increasing the impregnation temperature.
2018, 35(5): 1087-1094.
doi: 10.13801/j.cnki.fhclxb.20170612.001
Abstract:
Surface modifications of nano-hydroxyapatite (n-HA) were conducted in this study by using citric acid and stearic acid, respectively. The effects of different modifiers on the properties of n-HA were characterized by TGA, FTIR, XPS, and etc. The relevant results show that both citric acid and stearic acid could be successfully grafted onto the surface of hydroxyapatite, while the grafting ratio of stearic acidis relatively higher than that of citric acid. The composites were prepared by mixing PLA matrix with citric acid grafted n-HA.Through SEM, it is observed that the as-prepared composites containing n-HA powders less than 20wt% possess a uniform dispersibility and good inorganic/organic interfacial adhesion.The porous scaffold consisting of n-HA/PLA composites was prepared by 3D printing craft. The mechanical property evaluation results indicate that the as-prepared n-HA/PLA scaffold obtained from the fused deposition modeling 3D printing technique has a satisfactory compression modulus, although its compressive strength at 10% deformation is relatively lower than that of neat PLA scaffold.
Surface modifications of nano-hydroxyapatite (n-HA) were conducted in this study by using citric acid and stearic acid, respectively. The effects of different modifiers on the properties of n-HA were characterized by TGA, FTIR, XPS, and etc. The relevant results show that both citric acid and stearic acid could be successfully grafted onto the surface of hydroxyapatite, while the grafting ratio of stearic acidis relatively higher than that of citric acid. The composites were prepared by mixing PLA matrix with citric acid grafted n-HA.Through SEM, it is observed that the as-prepared composites containing n-HA powders less than 20wt% possess a uniform dispersibility and good inorganic/organic interfacial adhesion.The porous scaffold consisting of n-HA/PLA composites was prepared by 3D printing craft. The mechanical property evaluation results indicate that the as-prepared n-HA/PLA scaffold obtained from the fused deposition modeling 3D printing technique has a satisfactory compression modulus, although its compressive strength at 10% deformation is relatively lower than that of neat PLA scaffold.
2018, 35(5): 1095-1104.
doi: 10.13801/j.cnki.fhclxb.20170706.002
Abstract:
Based on carbon fiber reinforced resin composites IM7/CYCOM5320-1 out-of-autoclave (OOA) prepreg, the laying process in automated fiber placement(AFP) was analyzed. The optimized process parameters in AFP were obtained. The cure kinetic and visocosity behavoir of CYCOM5230-1 resin were analyzed. A short time cure cycle was developed. Properties of OOA composite made by the developed cure cycle were evaluated. The result shows that gaps defects induced by laying process will result in voids in the final composite part. By adjusting the distance of adjacent prepreg tows, as well as the process parameters(compaction force of 180 N, heating temperature of 50℃, laying speed of 0.20 m/s), the final composite part shows an even surface and good quality. Thermal analysis reveals that CYCOM5230-1 resin has a high viscosity at room temperature, which is benefit for air evacuation in out-of-autoclave process. The short time cure cycle improves production rate. The OOA composite made by the short time cure cycle can reach the similar fiber volume fraction of 59% and porosity of 0.5%, while compared to the traditional cure cycle. In addition, the composite manufactured by the short time cure cycle has the comparable quality of autoclave composite.
Based on carbon fiber reinforced resin composites IM7/CYCOM5320-1 out-of-autoclave (OOA) prepreg, the laying process in automated fiber placement(AFP) was analyzed. The optimized process parameters in AFP were obtained. The cure kinetic and visocosity behavoir of CYCOM5230-1 resin were analyzed. A short time cure cycle was developed. Properties of OOA composite made by the developed cure cycle were evaluated. The result shows that gaps defects induced by laying process will result in voids in the final composite part. By adjusting the distance of adjacent prepreg tows, as well as the process parameters(compaction force of 180 N, heating temperature of 50℃, laying speed of 0.20 m/s), the final composite part shows an even surface and good quality. Thermal analysis reveals that CYCOM5230-1 resin has a high viscosity at room temperature, which is benefit for air evacuation in out-of-autoclave process. The short time cure cycle improves production rate. The OOA composite made by the short time cure cycle can reach the similar fiber volume fraction of 59% and porosity of 0.5%, while compared to the traditional cure cycle. In addition, the composite manufactured by the short time cure cycle has the comparable quality of autoclave composite.
2018, 35(5): 1105-1113.
doi: 10.13801/j.cnki.fhclxb.20170802.001
Abstract:
The dynamic mechanical analysis (DMA) for hollow for glass microsphere(HGM)/epoxy resin composite was conducted. The temperature-dependent mechanical properties were given for HGM/epoxy resin composite. The storage and loss moduli master curves for HGM/epoxy resin composite were presented through application of the time-temperature superposition on measurements at a series of temperatures. The influence of temperature, frequency, volume ratio and particle size on the storage and loss modalus was analyzed, and the influence mechanism was investigated by SEM for HGM/epoxy resin composite. It is found that the storage and loss moduli of the composite both increase as the HGM volume fraction is increased. The storage modulus decreases with the increasing temperature, the loss modulus initially increases significantly with temperature and then decreases, forming a peak near the glass transition temperature for HGM/epoxy resin composite. Ratio of less than 10% is good to improve its dynamic mechanical properties. The agglomeration of particles and the adhesion of the interface have great influence on the dynamic mechanical properties of HGM/epoxy resin composites.
The dynamic mechanical analysis (DMA) for hollow for glass microsphere(HGM)/epoxy resin composite was conducted. The temperature-dependent mechanical properties were given for HGM/epoxy resin composite. The storage and loss moduli master curves for HGM/epoxy resin composite were presented through application of the time-temperature superposition on measurements at a series of temperatures. The influence of temperature, frequency, volume ratio and particle size on the storage and loss modalus was analyzed, and the influence mechanism was investigated by SEM for HGM/epoxy resin composite. It is found that the storage and loss moduli of the composite both increase as the HGM volume fraction is increased. The storage modulus decreases with the increasing temperature, the loss modulus initially increases significantly with temperature and then decreases, forming a peak near the glass transition temperature for HGM/epoxy resin composite. Ratio of less than 10% is good to improve its dynamic mechanical properties. The agglomeration of particles and the adhesion of the interface have great influence on the dynamic mechanical properties of HGM/epoxy resin composites.
2018, 35(5): 1114-1122.
doi: 10.13801/j.cnki.fhclxb.20170707.001
Abstract:
In order to study the flexural fatigue behavior of glass fiber reinforced polymer(GFRP)-Balsa sandwich beams prepared by a vacuum assisted resin infusion process, four-point fatigue bending tests for 42 specimens under different load levels were carried out. The fatigue failure modes, fatigue life and damage evolution of the sandwich beams were obtained. The damage mechanism of the three types of sandwich beams under bending fatigue load was analyzed. The failure modes of the beams without lattice-web are unified for the core shear failure and debonding, while those of the beams with lattice-web reinforced are varies with the number of lattice-web and the load level, which is buckling or partial crushing of upper facesheet or tensile failure of lower facesheet. The fatigue load-life(S-N) curves of sandwich beams were fitted by exponential empirical model, and the life prediction formulas of three kinds of sandwich beams were obtained. The displacement evolution of the sandwich beams undergoes three stages of "transient fall-stable evolution-damage initiation to failure". Compared with the specimens without lattice-web, the lattice-web reinforced specimens have obvious signs before fatigue failure.
In order to study the flexural fatigue behavior of glass fiber reinforced polymer(GFRP)-Balsa sandwich beams prepared by a vacuum assisted resin infusion process, four-point fatigue bending tests for 42 specimens under different load levels were carried out. The fatigue failure modes, fatigue life and damage evolution of the sandwich beams were obtained. The damage mechanism of the three types of sandwich beams under bending fatigue load was analyzed. The failure modes of the beams without lattice-web are unified for the core shear failure and debonding, while those of the beams with lattice-web reinforced are varies with the number of lattice-web and the load level, which is buckling or partial crushing of upper facesheet or tensile failure of lower facesheet. The fatigue load-life(S-N) curves of sandwich beams were fitted by exponential empirical model, and the life prediction formulas of three kinds of sandwich beams were obtained. The displacement evolution of the sandwich beams undergoes three stages of "transient fall-stable evolution-damage initiation to failure". Compared with the specimens without lattice-web, the lattice-web reinforced specimens have obvious signs before fatigue failure.
2018, 35(5): 1123-1130.
doi: 10.13801/j.cnki.fhclxb.20170801.001
Abstract:
For restraining skin wrinkling and improve interfacial properties, a novel foam core sandwich structure was proposed by inserting glass fibre-reinforced plastic(GFRP) stiffeners attached to the sandwich skins. A vacuum-assisted resin infusion method was used to manufacture the sandwich panels. In-plane compression tests and double cantilever beam tests were conducted to compare their load-displacement curves and failure modes of stiffened specimens and non-stiffened specimens. The results of in-plane compression tests indicate that upon the insertion of stiffeners, the failure mode of the foam core sandwich composite structures change from inefficient skin wrinkling to efficient compressive microbuckling or global buckling. Compared to non-stiffened specimens, with the same dosage of glass fibre-reinforced plastic, the average failure load increases by 40.87% for length of 130 mm and 35.63% for length of 190 mm, respectively. The results of double cantilever beam tests indicate that the bridging fiber between skin and stiffener can effectively prevent the development of crack. Comparing with to non-stiffened specimens, the energy release rate increases by 57.35%.
For restraining skin wrinkling and improve interfacial properties, a novel foam core sandwich structure was proposed by inserting glass fibre-reinforced plastic(GFRP) stiffeners attached to the sandwich skins. A vacuum-assisted resin infusion method was used to manufacture the sandwich panels. In-plane compression tests and double cantilever beam tests were conducted to compare their load-displacement curves and failure modes of stiffened specimens and non-stiffened specimens. The results of in-plane compression tests indicate that upon the insertion of stiffeners, the failure mode of the foam core sandwich composite structures change from inefficient skin wrinkling to efficient compressive microbuckling or global buckling. Compared to non-stiffened specimens, with the same dosage of glass fibre-reinforced plastic, the average failure load increases by 40.87% for length of 130 mm and 35.63% for length of 190 mm, respectively. The results of double cantilever beam tests indicate that the bridging fiber between skin and stiffener can effectively prevent the development of crack. Comparing with to non-stiffened specimens, the energy release rate increases by 57.35%.
2018, 35(5): 1131-1138.
doi: 10.13801/j.cnki.fhclxb.20170814.001
Abstract:
Artificial lightning strike testing was performed on a series of carbon woven fabric/epoxy laminate with metal fastener, and damage was assessed using visual inspection, ultrasonic testing, micro X-ray inspection and high-power microscope to analyze the damage mode, damage mechanism and damage characteristic of composite laminate with metal fastener under lightning current direct effect, meanwhile, mechanical property degradation extent of composite laminate with metal fastener was also assessed using material mechanical property test system. Research results indicate that due to the lightning current distributing effect aroused by mental fastener, delamination is the mainly damage mode of composite laminate with metal fastener when subjected to lightning strike, and it is distributed along the whole thickness direction of laminate. There is a lightning current intensity threshold about whether composite laminate with metal fastener occurs lightning strike damage, and when the lightning current intensity is lower than it, composite laminate with metal fastener will not appear lightning strike damage. During the process of static tension, because lightning strike damage around fastener hole will arouse the effect of stress distribution, the tensile loading capacity of composite laminate with metal fastener with lightning strike damage increases first and then decreases with the increasing lightning peak current.
Artificial lightning strike testing was performed on a series of carbon woven fabric/epoxy laminate with metal fastener, and damage was assessed using visual inspection, ultrasonic testing, micro X-ray inspection and high-power microscope to analyze the damage mode, damage mechanism and damage characteristic of composite laminate with metal fastener under lightning current direct effect, meanwhile, mechanical property degradation extent of composite laminate with metal fastener was also assessed using material mechanical property test system. Research results indicate that due to the lightning current distributing effect aroused by mental fastener, delamination is the mainly damage mode of composite laminate with metal fastener when subjected to lightning strike, and it is distributed along the whole thickness direction of laminate. There is a lightning current intensity threshold about whether composite laminate with metal fastener occurs lightning strike damage, and when the lightning current intensity is lower than it, composite laminate with metal fastener will not appear lightning strike damage. During the process of static tension, because lightning strike damage around fastener hole will arouse the effect of stress distribution, the tensile loading capacity of composite laminate with metal fastener with lightning strike damage increases first and then decreases with the increasing lightning peak current.
2018, 35(5): 1139-1148.
doi: 10.13801/j.cnki.fhclxb.20170821.002
Abstract:
With a distinct structure that is fully integrated, three-dimensional braided composites not only overcome the defects in laminated composites which have relatively poor mechanical properties in the thickness direction and are prone to interlaminar delamination, but also are superior in high strength-to-mass and stiffness-to-weight ratios, improved impact resistance and damage tolerance as compared with traditional metal materials. Owing to these merits, they also have broad potential applications in automobile, high-speed train, navigation, aviation, and aerospace industries. Plate specimens of three-dimensional four-directional braided composite(3D4DBCo) were designed and impacted at different locations by the steel ball with an approximate initial velocity of 210 m/s with the help of the air gun experiment system in this paper. On the basis of macroscopic and microscopic observation, the damage morphology and the failure mechanism of 3D4DBCo subjected to high speed impact of the steel balls were analyzed and summed up. What's more, the macro-level continuum damage mechanics (CDM) finite element model of 3D4DBCo was established, and the comparisons between numerical simulation and experiment results show highly agreement in residual velocity within 5%, as well as the damage characteristic, which validate the effectiveness of the macroscopic CDM finite element model.
With a distinct structure that is fully integrated, three-dimensional braided composites not only overcome the defects in laminated composites which have relatively poor mechanical properties in the thickness direction and are prone to interlaminar delamination, but also are superior in high strength-to-mass and stiffness-to-weight ratios, improved impact resistance and damage tolerance as compared with traditional metal materials. Owing to these merits, they also have broad potential applications in automobile, high-speed train, navigation, aviation, and aerospace industries. Plate specimens of three-dimensional four-directional braided composite(3D4DBCo) were designed and impacted at different locations by the steel ball with an approximate initial velocity of 210 m/s with the help of the air gun experiment system in this paper. On the basis of macroscopic and microscopic observation, the damage morphology and the failure mechanism of 3D4DBCo subjected to high speed impact of the steel balls were analyzed and summed up. What's more, the macro-level continuum damage mechanics (CDM) finite element model of 3D4DBCo was established, and the comparisons between numerical simulation and experiment results show highly agreement in residual velocity within 5%, as well as the damage characteristic, which validate the effectiveness of the macroscopic CDM finite element model.
2018, 35(5): 1149-1157.
doi: 10.13801/j.cnki.fhclxb.20170712.003
Abstract:
The technology of automated fiber placement (AFP) in-situ crystallization for thermoplastic composites is the key point for efficiently and inexpensively manufacturing large composite components. However, because the processing parameters have a great influence on the mechanical properties, to ensure the mechanical properties of laminates made by AFP in situ crystallization, the processing parameters should be analyzed and optimized. The prepreg made of polypropylene as matrix and continuous glass fiber as reinforcement (GF/PP) was used to produce laminates through the AFP platform. Influences of the processing parameters, such as temperature of hot gas, lay-up pressure of hot roll and cold roll, and furthermore, their interaction effects on the mechanical properties were analyzed based on the theory of response surface methodology. A quadratic polynomial regression equation was set up to forecast the relationship between the processing parameters and the mechanical properties. The effectiveness and reliability of regression model were verified through the test analysis such as predicated versus actual. Furthermore, the optimal process parameters of AFP were obtained:temperature of hot gas is 385℃, lay-up pressure of hot roll is 0.3 MPa and lay-up pressure of cold roll is 1.1 MPa.
The technology of automated fiber placement (AFP) in-situ crystallization for thermoplastic composites is the key point for efficiently and inexpensively manufacturing large composite components. However, because the processing parameters have a great influence on the mechanical properties, to ensure the mechanical properties of laminates made by AFP in situ crystallization, the processing parameters should be analyzed and optimized. The prepreg made of polypropylene as matrix and continuous glass fiber as reinforcement (GF/PP) was used to produce laminates through the AFP platform. Influences of the processing parameters, such as temperature of hot gas, lay-up pressure of hot roll and cold roll, and furthermore, their interaction effects on the mechanical properties were analyzed based on the theory of response surface methodology. A quadratic polynomial regression equation was set up to forecast the relationship between the processing parameters and the mechanical properties. The effectiveness and reliability of regression model were verified through the test analysis such as predicated versus actual. Furthermore, the optimal process parameters of AFP were obtained:temperature of hot gas is 385℃, lay-up pressure of hot roll is 0.3 MPa and lay-up pressure of cold roll is 1.1 MPa.
2018, 35(5): 1158-1165.
doi: 10.13801/j.cnki.fhclxb.20170713.001
Abstract:
Composites are widely used in the aircraft structure and its damage tolerance property is an important index of aircraft design. An empirical prediction formula for compressive strength of composite laminate after impact based on energy was formulated. With experimental studies, influence factors for compressive strength were analyzed to determine the forms and parameters of the empirical formula, and the predicted results were compared with experimental data as well. The predicted results of the empirical method accord well with sufficient experimental data by general verification. The results indicate that it is a convenient and efficient engineering prediction method for compressive strength after impact. In addition, the experimental results indicate that the relationships between compressive strength and impact energy are suitable for piecewise power function fitting. Impact energy, thickness of laminate, ply proportion and material tenacity have obvious effect on compressive strength of composite laminate after impact, while the diameter of impactor has no significant effect.
Composites are widely used in the aircraft structure and its damage tolerance property is an important index of aircraft design. An empirical prediction formula for compressive strength of composite laminate after impact based on energy was formulated. With experimental studies, influence factors for compressive strength were analyzed to determine the forms and parameters of the empirical formula, and the predicted results were compared with experimental data as well. The predicted results of the empirical method accord well with sufficient experimental data by general verification. The results indicate that it is a convenient and efficient engineering prediction method for compressive strength after impact. In addition, the experimental results indicate that the relationships between compressive strength and impact energy are suitable for piecewise power function fitting. Impact energy, thickness of laminate, ply proportion and material tenacity have obvious effect on compressive strength of composite laminate after impact, while the diameter of impactor has no significant effect.
2018, 35(5): 1166-1171.
doi: 10.13801/j.cnki.fhclxb.20170808.001
Abstract:
Airship envelope fabrics are functional laminated weave composites that behaved rather complicated nonlinear mechanical characteristics. An accurate mechanical model is the base for structural design and numerical analysis. The biaxial tensile tests of airship envelope specimens were carried out at seven tensile stress ratios. On the basis of orthotropic composites theory, the elastic engineering constants were calculated by the method of minimization of the sum of square of the strain residuals and the linear mechanical model was presented. The response surfaces of stress-elastic constants could be generated subsequently and the complete three-order polynomials nonlinear mechanical model was finally proposed in terms of stress variable. The numerical simulation of biaxial tensile at seven ratios was proposed and the results are in good agreement with the tests situation on the distributions of stress and the deformations of the slit. The stress-strain curves of simulation were compared with the experimental ones and show good consistency. In this case, the mechanical model is accurate enough for airship structural analysis.
Airship envelope fabrics are functional laminated weave composites that behaved rather complicated nonlinear mechanical characteristics. An accurate mechanical model is the base for structural design and numerical analysis. The biaxial tensile tests of airship envelope specimens were carried out at seven tensile stress ratios. On the basis of orthotropic composites theory, the elastic engineering constants were calculated by the method of minimization of the sum of square of the strain residuals and the linear mechanical model was presented. The response surfaces of stress-elastic constants could be generated subsequently and the complete three-order polynomials nonlinear mechanical model was finally proposed in terms of stress variable. The numerical simulation of biaxial tensile at seven ratios was proposed and the results are in good agreement with the tests situation on the distributions of stress and the deformations of the slit. The stress-strain curves of simulation were compared with the experimental ones and show good consistency. In this case, the mechanical model is accurate enough for airship structural analysis.
2018, 35(5): 1172-1181.
doi: 10.13801/j.cnki.fhclxb.20170808.003
Abstract:
Based on the evolution of magneto-induced microstructure by particle dynamics simulation, the 3D geometric model was established for transversely isotropic magnetorheological elastomers(MREs). On the basis of the current two main theories for the interaction between magnetic particles, the control equations on particles were built considering the coupling effect between deformation and magnetic field. The mechanics-magnetic coupling properties were studied in the mesoscopic level by establishing the multi-particles numerical model of MREs. The comparison result between numerical model and shear experiments indicates that multipole force model is closer to the test data than point-dipoles model. The influences of magnetic flux density and particle volume fraction on magneto-induced shear modulus were also discussed, that is, the numerical model gives an excellent agreement with experiments. The optimum particle volume fraction for the largest relative magnetorheological effect is about 20%.
Based on the evolution of magneto-induced microstructure by particle dynamics simulation, the 3D geometric model was established for transversely isotropic magnetorheological elastomers(MREs). On the basis of the current two main theories for the interaction between magnetic particles, the control equations on particles were built considering the coupling effect between deformation and magnetic field. The mechanics-magnetic coupling properties were studied in the mesoscopic level by establishing the multi-particles numerical model of MREs. The comparison result between numerical model and shear experiments indicates that multipole force model is closer to the test data than point-dipoles model. The influences of magnetic flux density and particle volume fraction on magneto-induced shear modulus were also discussed, that is, the numerical model gives an excellent agreement with experiments. The optimum particle volume fraction for the largest relative magnetorheological effect is about 20%.
2018, 35(5): 1182-1191.
doi: 10.13801/j.cnki.fhclxb.20170821.005
Abstract:
In this paper, a polystyrene (PS)-supercritical CO2 system was used herein as a case example to simulate bubble growth behavior and cooling and solidification. The mathematical model based on the cell model was established to solve momentum equation, mass equation and diffusion equation. The software program of system simulation based on the above mathematical model was compiled with MATLAB language. In the process of simulation, the quantitative relationship between process parameters and microcellular morphology was determined by introducing the relationship between the material properties and the temperature, pressure and CO2 concentration. The results show that CO2 concentration has the greatest effect on bubble growth, and the effect of temperature is the least for the PS-CO2 system. According to the simulation of orthogonal, under different processing conditions, the maximum value of bubble radius is 49.5 μm, the minimum value is 1.27 μm, and the suitable bubble radius for microcellular foaming is between 10 μm and 25 μm. In addition, the study of the bubble cooling shows that the increase of cooling rate will increase the bubble density and reduce the bubble size.
In this paper, a polystyrene (PS)-supercritical CO2 system was used herein as a case example to simulate bubble growth behavior and cooling and solidification. The mathematical model based on the cell model was established to solve momentum equation, mass equation and diffusion equation. The software program of system simulation based on the above mathematical model was compiled with MATLAB language. In the process of simulation, the quantitative relationship between process parameters and microcellular morphology was determined by introducing the relationship between the material properties and the temperature, pressure and CO2 concentration. The results show that CO2 concentration has the greatest effect on bubble growth, and the effect of temperature is the least for the PS-CO2 system. According to the simulation of orthogonal, under different processing conditions, the maximum value of bubble radius is 49.5 μm, the minimum value is 1.27 μm, and the suitable bubble radius for microcellular foaming is between 10 μm and 25 μm. In addition, the study of the bubble cooling shows that the increase of cooling rate will increase the bubble density and reduce the bubble size.
2018, 35(5): 1192-1202.
doi: 10.13801/j.cnki.fhclxb.20170727.003
Abstract:
Yarns in the thin-walled plain woven composites are not homogeneous through the thickness, and hence there are noticeable discrepancies between the bending stiffnesses obtaied from engineering constants and the experimental results. A direct micromechanical method for predicting bending stiffnesses has been proposed here using the unit-cell finite element model. The path of the yarn center was taken to be periodic cubic bézier curve, and the 3D geometry model of a unit-cell was obtained assuming that the yarns enjoy constant cross section with a lenticular shape. The periodic boundary conditions for bending and twisting conditions were presented. Combing the cubic voxel mesh method, the non-uniform distributed displacement fields were applied by coupling the freedom degrees of the opposite points one by one. The tension, four-point bending and cantilever plate bending tests were conducted. The results indicate that the provided unit-cell finite element model can predict the bending stiffnesses precisely. As to the bending configuration of the cantilever plate, comparing with the results obtained from engineering constants, the results depending on the predicted stiffnesses agree better with the test.
Yarns in the thin-walled plain woven composites are not homogeneous through the thickness, and hence there are noticeable discrepancies between the bending stiffnesses obtaied from engineering constants and the experimental results. A direct micromechanical method for predicting bending stiffnesses has been proposed here using the unit-cell finite element model. The path of the yarn center was taken to be periodic cubic bézier curve, and the 3D geometry model of a unit-cell was obtained assuming that the yarns enjoy constant cross section with a lenticular shape. The periodic boundary conditions for bending and twisting conditions were presented. Combing the cubic voxel mesh method, the non-uniform distributed displacement fields were applied by coupling the freedom degrees of the opposite points one by one. The tension, four-point bending and cantilever plate bending tests were conducted. The results indicate that the provided unit-cell finite element model can predict the bending stiffnesses precisely. As to the bending configuration of the cantilever plate, comparing with the results obtained from engineering constants, the results depending on the predicted stiffnesses agree better with the test.
2018, 35(5): 1203-1210.
doi: 10.13801/j.cnki.fhclxb.20170829.001
Abstract:
In order to establish the constitutive model of solid composite propellants with damage, at a mesoscopic scale, the damage of the material was considered in a micro-cracking form, and the crack density was chosen as internal damage variable. On the basis of Abdel-Tawab's constitutive equation, the damage mapping tensor which was derived in a general form by using the homogeneous theory of microcracks. Usually, the damage mapping tensor is minor symmetric, and its physical significance is that mapping a multiaxial loading on an anisotropic material in true stress space into a more complicated multiaxial loading on an isotropic material in effective stress space. Secondly, a damage evolution equation was obtained based on the dynamic model of crack growth in viscoelastic material and the concept of crack growth resistance curves. There are only four micro-parameters which have clear physical meanings and similar variation tendencies with macro-stress curves in damage evolution equation. Numerical results indicate that the model can correctly reflect the anisotropic damage feature of material, the dependence of damage on strain rate and temperature, and the capacity to predict creep damage behavior reasonably.
In order to establish the constitutive model of solid composite propellants with damage, at a mesoscopic scale, the damage of the material was considered in a micro-cracking form, and the crack density was chosen as internal damage variable. On the basis of Abdel-Tawab's constitutive equation, the damage mapping tensor which was derived in a general form by using the homogeneous theory of microcracks. Usually, the damage mapping tensor is minor symmetric, and its physical significance is that mapping a multiaxial loading on an anisotropic material in true stress space into a more complicated multiaxial loading on an isotropic material in effective stress space. Secondly, a damage evolution equation was obtained based on the dynamic model of crack growth in viscoelastic material and the concept of crack growth resistance curves. There are only four micro-parameters which have clear physical meanings and similar variation tendencies with macro-stress curves in damage evolution equation. Numerical results indicate that the model can correctly reflect the anisotropic damage feature of material, the dependence of damage on strain rate and temperature, and the capacity to predict creep damage behavior reasonably.
2018, 35(5): 1211-1218.
doi: 10.13801/j.cnki.fhclxb.20170623.001
Abstract:
The fly ash cenospheres(FAC)/Mg alloy dissolvable composites with different contents of Al were prepared by stirring cast method. Optical microscopy, SEM and XRD were used to study the microstructure, surface morphology after the dissolution and phases of the dissolution product of the FAC/Mg alloy dissolvable composites. The compression property of the FAC/Mg alloy composite was tested using a mechanical performance testing machine. The electrochemical properties were investigated using electrochemical workstation. The immersion tests of the composites were conducted in potassium chloride (KCl) solution at different temperatures. The results show that the FAC/Mg alloy dissolvable composites are mainly composed of α-Mg matrix, β-Mg17Al12 phase, Mg2Si phase and MgO phase. The dissolving rate of the FAC/Mg alloy dissolvable composites first enhances and then weakens with the increase of the content of Al. When the content of Al is 15wt%, the FAC/Mg alloy composite has the fastest dissolving rate of 56 mg/(h·cm2) in 3wt% potassium chloride (KCl) at 80℃.The compression strength of FAC/Mg alloy dissolvable composites first increases and then decreases with the increase of Al content, and the compression strengths of the FAC/Mg alloy composites are higher than 300 MPa, the highest strength is 372 MPa.
The fly ash cenospheres(FAC)/Mg alloy dissolvable composites with different contents of Al were prepared by stirring cast method. Optical microscopy, SEM and XRD were used to study the microstructure, surface morphology after the dissolution and phases of the dissolution product of the FAC/Mg alloy dissolvable composites. The compression property of the FAC/Mg alloy composite was tested using a mechanical performance testing machine. The electrochemical properties were investigated using electrochemical workstation. The immersion tests of the composites were conducted in potassium chloride (KCl) solution at different temperatures. The results show that the FAC/Mg alloy dissolvable composites are mainly composed of α-Mg matrix, β-Mg17Al12 phase, Mg2Si phase and MgO phase. The dissolving rate of the FAC/Mg alloy dissolvable composites first enhances and then weakens with the increase of the content of Al. When the content of Al is 15wt%, the FAC/Mg alloy composite has the fastest dissolving rate of 56 mg/(h·cm2) in 3wt% potassium chloride (KCl) at 80℃.The compression strength of FAC/Mg alloy dissolvable composites first increases and then decreases with the increase of Al content, and the compression strengths of the FAC/Mg alloy composites are higher than 300 MPa, the highest strength is 372 MPa.
2018, 35(5): 1219-1226.
doi: 10.13801/j.cnki.fhclxb.20170727.002
Abstract:
The machining surface of SiCP/Al composites contains of lots of bumps, potholes and defects, leading to the confusion of roughness and defect information and unreasonable evaluation of the machining surface. In order to extracting the surface roughness and evaluating of the machining surface of SiCP/Al composites reasonably, a filtering method based on dual tree complex wavelet transform(DT-CWT) was put forward in this paper. The least squares method, Gaussian filtering method and the filtering method based on DT-CWT were adopted to extract the information of surface roughness and evaluated from two aspects including stability and degree of influence by defects. The results show that filtering method based on DT-CWT has high stability and can distinguish surface roughness from defect information more effectively. Therefore, it is more suitable for the extract of the surface roughness of SiCP/Al composites. According to comparison between the machining surface of SiCP/Al whose Al-matrix includes of 2024 and 6063 aluminum alloy by the filtering method base on DT-CWT, it is found that the quality of 2024 aluminum matrix composite surface is better than that of 6063 aluminum composite.
The machining surface of SiCP/Al composites contains of lots of bumps, potholes and defects, leading to the confusion of roughness and defect information and unreasonable evaluation of the machining surface. In order to extracting the surface roughness and evaluating of the machining surface of SiCP/Al composites reasonably, a filtering method based on dual tree complex wavelet transform(DT-CWT) was put forward in this paper. The least squares method, Gaussian filtering method and the filtering method based on DT-CWT were adopted to extract the information of surface roughness and evaluated from two aspects including stability and degree of influence by defects. The results show that filtering method based on DT-CWT has high stability and can distinguish surface roughness from defect information more effectively. Therefore, it is more suitable for the extract of the surface roughness of SiCP/Al composites. According to comparison between the machining surface of SiCP/Al whose Al-matrix includes of 2024 and 6063 aluminum alloy by the filtering method base on DT-CWT, it is found that the quality of 2024 aluminum matrix composite surface is better than that of 6063 aluminum composite.
2018, 35(5): 1227-1235.
doi: 10.13801/j.cnki.fhclxb.20170627.001
Abstract:
In this contribution, numerical modeling was performed to interpret the effects of gradient microstructure on the tensile behaviors of Ti46Zr20V12Cu5Be17 metallic glass(MG). The free volume theory was incorporated into the ABAQUS code as a user material subroutine UMAT, which was used to depict the shear banding evolution in the MG matrix. Particles and initial free volume were assumed to be distributed in form of various gradient functions, and the resulting material models were loaded under uniaxial tension. The results show that the tensile plasticity of MG matrix composites containing groove shape gradient distribution of particle is best, and appear necking deformation during plastic deformation; For the initial free volume containing the convex gradient distribution, MG plastic is improved well; When the free volume gradient distribution span is changed, the smaller gradient span in MG, the more obvious plastic is increased; And as for particles, the number of plies on both sides is more, the main shear zone through in the sample is not easy to appear during plastic deformation.
In this contribution, numerical modeling was performed to interpret the effects of gradient microstructure on the tensile behaviors of Ti46Zr20V12Cu5Be17 metallic glass(MG). The free volume theory was incorporated into the ABAQUS code as a user material subroutine UMAT, which was used to depict the shear banding evolution in the MG matrix. Particles and initial free volume were assumed to be distributed in form of various gradient functions, and the resulting material models were loaded under uniaxial tension. The results show that the tensile plasticity of MG matrix composites containing groove shape gradient distribution of particle is best, and appear necking deformation during plastic deformation; For the initial free volume containing the convex gradient distribution, MG plastic is improved well; When the free volume gradient distribution span is changed, the smaller gradient span in MG, the more obvious plastic is increased; And as for particles, the number of plies on both sides is more, the main shear zone through in the sample is not easy to appear during plastic deformation.
2018, 35(5): 1236-1243.
doi: 10.13801/j.cnki.fhclxb.20170713.003
Abstract:
With Ce-La-TiO2 hollow microspheres and hexadecanol (H)-palmitic acid (PA)-lauric acid (LA) as carrier material and phase change material respectively, H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites were made by sol-gel method and the vacuum adsorption method. By combining the uniform design and radial basis function(RBF) neural network, the effect of preparation factors (i.e. speed of the magnetic stirring, temperature of constant temperature reflow, rate of increase in calcining and vacuum degree of vacuum thermostatic oven) on particle size distribution of the H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites was investigated experimentally. In addition, the H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites with optimal uniform particle size distribution was tested and characterized. The results show that RBF neural network has the best approximation effect when spreading coefficient is 0.45~0.55. To obtain H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites with optimal uniform particle size distribution, the preparation parameters were identified as follows:magnetic stirring speed of 1 762 r/min, temperature of constant temperature reflow of 66.9℃, increase rate in calcining of 2.43℃/min and vacuum of vacuum thermostatic oven of 0.58 MPa. On the base of the above preparation parameters, median diameter d50 is 190.02 nm, the measured value of particle size distribution range is 180.50 nm. The measured value agrees well with the predictive value (relative error is 3.58%). In the case of relative humidity between 35% and 85%, the equilibrium moisture content is obtained to be between 0.0369 g/g and 0.1702 g/g, phase transition temperature between 24.21℃ and 29.48℃, phase change enthalpy between 31.24 J/g and 33.07 J/g, and formaldehyde degradation rate reaches 56.92% after 5 h.
With Ce-La-TiO2 hollow microspheres and hexadecanol (H)-palmitic acid (PA)-lauric acid (LA) as carrier material and phase change material respectively, H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites were made by sol-gel method and the vacuum adsorption method. By combining the uniform design and radial basis function(RBF) neural network, the effect of preparation factors (i.e. speed of the magnetic stirring, temperature of constant temperature reflow, rate of increase in calcining and vacuum degree of vacuum thermostatic oven) on particle size distribution of the H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites was investigated experimentally. In addition, the H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites with optimal uniform particle size distribution was tested and characterized. The results show that RBF neural network has the best approximation effect when spreading coefficient is 0.45~0.55. To obtain H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites with optimal uniform particle size distribution, the preparation parameters were identified as follows:magnetic stirring speed of 1 762 r/min, temperature of constant temperature reflow of 66.9℃, increase rate in calcining of 2.43℃/min and vacuum of vacuum thermostatic oven of 0.58 MPa. On the base of the above preparation parameters, median diameter d50 is 190.02 nm, the measured value of particle size distribution range is 180.50 nm. The measured value agrees well with the predictive value (relative error is 3.58%). In the case of relative humidity between 35% and 85%, the equilibrium moisture content is obtained to be between 0.0369 g/g and 0.1702 g/g, phase transition temperature between 24.21℃ and 29.48℃, phase change enthalpy between 31.24 J/g and 33.07 J/g, and formaldehyde degradation rate reaches 56.92% after 5 h.
2018, 35(5): 1244-1252.
doi: 10.13801/j.cnki.fhclxb.20170619.001
Abstract:
Oleic acid (OA) decorated Cu2O microcrystals/paraffin wax (Cu2O-OA/PW) composites were synthesized by thermal decomposition of Cu (Ⅱ) formate-octylamine complexes in the PW using OA as a dispersing agent. The phase structure, morphology, chemical state and phase transition behavior were investigated by means of XRD, SEM, TEM, FTIR and DSC. The thermal sensitivity, thermal expansion and thermal stability of composites were also investigated. The results show that rhombic dodecahedron and cubic Cu2O microcrystals are synthesized by changing OA concentration and precursor concentration. OA molecules are adsorbed on Cu2O microcrystals by chemisorption way. The latent heats of Cu2O-OA/PW composites shift to lower values compared to those of pure PW; however, the melting and freezing temperatures are kept almost the same as pure PW. With the increase of precursor concentration, the thermosensitivity of Cu2O-OA/PW composites increases significantly, but the volume expansibility of composites decreases. There is no sediment in Cu2O-OA/PW composites after being heated for many times, reflecting its excellent thermal stability.
Oleic acid (OA) decorated Cu2O microcrystals/paraffin wax (Cu2O-OA/PW) composites were synthesized by thermal decomposition of Cu (Ⅱ) formate-octylamine complexes in the PW using OA as a dispersing agent. The phase structure, morphology, chemical state and phase transition behavior were investigated by means of XRD, SEM, TEM, FTIR and DSC. The thermal sensitivity, thermal expansion and thermal stability of composites were also investigated. The results show that rhombic dodecahedron and cubic Cu2O microcrystals are synthesized by changing OA concentration and precursor concentration. OA molecules are adsorbed on Cu2O microcrystals by chemisorption way. The latent heats of Cu2O-OA/PW composites shift to lower values compared to those of pure PW; however, the melting and freezing temperatures are kept almost the same as pure PW. With the increase of precursor concentration, the thermosensitivity of Cu2O-OA/PW composites increases significantly, but the volume expansibility of composites decreases. There is no sediment in Cu2O-OA/PW composites after being heated for many times, reflecting its excellent thermal stability.
2018, 35(5): 1253-1259.
doi: 10.13801/j.cnki.fhclxb.20170814.004
Abstract:
Reduced graphene oxide (RGO) was synthesized via chemical reduction of graphene oxide (GO) with hydrazine hydrate. By adding RGO in blending system of the natural rubber(NR) and nitrile butadiene rubber(NBR), the RGO/NR-NBR composites were prepared by latex co-coagulation method. The structure and morphology of RGO were analyzed by FTIR, Raman spectroscopy, XRD and SEM. The results show that oxygen functional group can be removed by the reduction of GO with hydrazine hydrate, meanwhile, RGO has maintained the monolayer structure of GO. SEM images of RGO/NB-NBR composites indicate that RGO is homogeneously dispersed in composites and the stretching section of composites becomes rough obviously. Analysis on vulcanization characteristics indicate that the cross-linking density, maximum torque and torque difference of the RGO/NR-NBR composite increase with the RGO mass fraction increasing. The mechanical properties of RGO/NR-NBR compsites have been greatly improved after the addition of RGO. When RGO/NR-NBR composites with 3.0% RGO, the tensile strength, tensile strength at 100% elongation and the shore A hardness of RGO/NR-NBR composites increase by 65.7%, 90.3% and 21.1%, respectively; the elongation at break decreases by 13.1%.
Reduced graphene oxide (RGO) was synthesized via chemical reduction of graphene oxide (GO) with hydrazine hydrate. By adding RGO in blending system of the natural rubber(NR) and nitrile butadiene rubber(NBR), the RGO/NR-NBR composites were prepared by latex co-coagulation method. The structure and morphology of RGO were analyzed by FTIR, Raman spectroscopy, XRD and SEM. The results show that oxygen functional group can be removed by the reduction of GO with hydrazine hydrate, meanwhile, RGO has maintained the monolayer structure of GO. SEM images of RGO/NB-NBR composites indicate that RGO is homogeneously dispersed in composites and the stretching section of composites becomes rough obviously. Analysis on vulcanization characteristics indicate that the cross-linking density, maximum torque and torque difference of the RGO/NR-NBR composite increase with the RGO mass fraction increasing. The mechanical properties of RGO/NR-NBR compsites have been greatly improved after the addition of RGO. When RGO/NR-NBR composites with 3.0% RGO, the tensile strength, tensile strength at 100% elongation and the shore A hardness of RGO/NR-NBR composites increase by 65.7%, 90.3% and 21.1%, respectively; the elongation at break decreases by 13.1%.
2018, 35(5): 1260-1268.
doi: 10.13801/j.cnki.fhclxb.20170620.001
Abstract:
As a kind of promising cathode materials of supercapacitor, MnO2 has higher theoretical capacitance and better cycle stability, but its application is limited by poorer electronic conductivity. The reduced graphene oxide (RGO)/NixMn1-x/2O2 composites were synthesized by hydrothermal method. The phase composition, microstructure and electrochemical properties of the prepared RGO/NixMn1-x/2O2 composites were characterized by XRD, SEM, TEM, FTIR and electrochemical analysis. The electrochemical tests show that, the capacitor performance of MnO2 is enhanced by partial substitution of Mn by Ni. The specific capacitance of MnO2 synthesized by hydrothermal method is 66 F/g (scanning speed is 10 mV/s), when x=0.02, the specific capacitance of Ni0.02Mn0.99O2 is 111 F/g. When the RGO is added, the capacitance performance of RGO/NixMn1-x/2O2 composites is further improved. As a result, the specific capacitance of 2wt% RGO/Ni0.02Mn0.99O2 is 136 F/g. The addition of RGO increases the electron mobility of the active materials. Meanwhile, the conductivity is enhanced because of the doping of Ni, which results in the existence of appropriate point defects in the MnO2 lattice. The super capacitor with RGO/NixMn1-x/2O2 as the cathode material has advantages of electrical double-layer capacitor and faradaic pseudocapacitor at the same time. The electrochemical properties of RGO/NixMn1-x/2O2 composites are enhanced by the synergistic action of doping of Ni ions and loading of RGO.
As a kind of promising cathode materials of supercapacitor, MnO2 has higher theoretical capacitance and better cycle stability, but its application is limited by poorer electronic conductivity. The reduced graphene oxide (RGO)/NixMn1-x/2O2 composites were synthesized by hydrothermal method. The phase composition, microstructure and electrochemical properties of the prepared RGO/NixMn1-x/2O2 composites were characterized by XRD, SEM, TEM, FTIR and electrochemical analysis. The electrochemical tests show that, the capacitor performance of MnO2 is enhanced by partial substitution of Mn by Ni. The specific capacitance of MnO2 synthesized by hydrothermal method is 66 F/g (scanning speed is 10 mV/s), when x=0.02, the specific capacitance of Ni0.02Mn0.99O2 is 111 F/g. When the RGO is added, the capacitance performance of RGO/NixMn1-x/2O2 composites is further improved. As a result, the specific capacitance of 2wt% RGO/Ni0.02Mn0.99O2 is 136 F/g. The addition of RGO increases the electron mobility of the active materials. Meanwhile, the conductivity is enhanced because of the doping of Ni, which results in the existence of appropriate point defects in the MnO2 lattice. The super capacitor with RGO/NixMn1-x/2O2 as the cathode material has advantages of electrical double-layer capacitor and faradaic pseudocapacitor at the same time. The electrochemical properties of RGO/NixMn1-x/2O2 composites are enhanced by the synergistic action of doping of Ni ions and loading of RGO.
2018, 35(5): 1269-1278.
doi: 10.13801/j.cnki.fhclxb.20170814.003
Abstract:
A new electric and porous material named raney nickel(RNi) was proposed as S immobilizer for lithium sulfur batteries. The solvent method, grinding high temperature method and ball milling high temperature method were introduced to prepare S/RNi composite. The results show S/RNi composite exhibits the best electrochemical performance under solvent method. The pretreated raney nickel is a spongy and conductive porous structure with a pore size distribution between 12.5 nm and 50 nm. SEM and XRD demonstrate that S/RNi composite has good pore structure under solvent method. Elemental sulfur grains are evenly distributed and in close contact in the pore structure of raney nickel with a small size. S/RNi cathode under solvent method performs an initial discharge specific capacity of 1 479 mAh/g, and still remains a discharge specific capacity of 765 mAh/g after 200 cycles with a high coulombic efficiency of about 99%. The cycling performance of S/RNi composite under solvent method is still better than that of conventional S/C composite. The cyclic stability and high rate performance of S/RNi cathode under solvent method are contributed to the conductivity and the chemical adsorption on polysulfides of raney nickel.
A new electric and porous material named raney nickel(RNi) was proposed as S immobilizer for lithium sulfur batteries. The solvent method, grinding high temperature method and ball milling high temperature method were introduced to prepare S/RNi composite. The results show S/RNi composite exhibits the best electrochemical performance under solvent method. The pretreated raney nickel is a spongy and conductive porous structure with a pore size distribution between 12.5 nm and 50 nm. SEM and XRD demonstrate that S/RNi composite has good pore structure under solvent method. Elemental sulfur grains are evenly distributed and in close contact in the pore structure of raney nickel with a small size. S/RNi cathode under solvent method performs an initial discharge specific capacity of 1 479 mAh/g, and still remains a discharge specific capacity of 765 mAh/g after 200 cycles with a high coulombic efficiency of about 99%. The cycling performance of S/RNi composite under solvent method is still better than that of conventional S/C composite. The cyclic stability and high rate performance of S/RNi cathode under solvent method are contributed to the conductivity and the chemical adsorption on polysulfides of raney nickel.
2018, 35(5): 1279-1287.
doi: 10.13801/j.cnki.fhclxb.20170620.002
Abstract:
The high crystalline single-walled carbon nanotubes(SWCNTs) were prepared by direct current arc-discharge method and the CoFe2O4 nanoparticles were prepared by sol-gel method. The double-layer composites for microwave absorption were fabricated by compositing SWCNTs and CoFe2O4. Their phase structures, surface morphologies and electromagnetic parameters were characterized by Raman spectrum, XRD, SEM, TEM and vector network analyzer. The microwave absorption properties of SWCNTs-CoFe2O4 double-layer composites were calculated according to transmission line theory in the frequency range of 2-18 GHz. The results show that the absorption property of SWCNTs-CoFe2O4 double-layer composites is improved greatly. The best reflection loss of SWCNTs-CoFe2O4 double-layer composite reaches -61.13 dB as the match layer is CoFe2O4 and the absorbing layer is SWCNTs. The absorbing bandwidth with the reflection loss values below -10 dB of SWCNTs-CoFe2O4 double-layer composites is 7 GHz which from 8 GHz to 15 GHz. SWCNTs-CoFe2O4 nanoparticles double-layer composites could be described as an excellent absorbing material with high reflection loss and broad absorbing bandwidth.
The high crystalline single-walled carbon nanotubes(SWCNTs) were prepared by direct current arc-discharge method and the CoFe2O4 nanoparticles were prepared by sol-gel method. The double-layer composites for microwave absorption were fabricated by compositing SWCNTs and CoFe2O4. Their phase structures, surface morphologies and electromagnetic parameters were characterized by Raman spectrum, XRD, SEM, TEM and vector network analyzer. The microwave absorption properties of SWCNTs-CoFe2O4 double-layer composites were calculated according to transmission line theory in the frequency range of 2-18 GHz. The results show that the absorption property of SWCNTs-CoFe2O4 double-layer composites is improved greatly. The best reflection loss of SWCNTs-CoFe2O4 double-layer composite reaches -61.13 dB as the match layer is CoFe2O4 and the absorbing layer is SWCNTs. The absorbing bandwidth with the reflection loss values below -10 dB of SWCNTs-CoFe2O4 double-layer composites is 7 GHz which from 8 GHz to 15 GHz. SWCNTs-CoFe2O4 nanoparticles double-layer composites could be described as an excellent absorbing material with high reflection loss and broad absorbing bandwidth.
2018, 35(5): 1288-1297.
doi: 10.13801/j.cnki.fhclxb.20170808.002
Abstract:
In order to make full use of the ground circulating fluidized bed combustion slag (CFB), reactive MgO, CFB and silica fume (SF) were used to prepare MgO-CFB-SF composites. The good fluidity, high strength and low cost MgO-CFB-SF composites were gained. The effects of curing temperature, SF and MgO dosage on the strength, reaction products and microstructures of MgO-CFB-SF were investigated. The effect of MgO's activity and fineness on compressive strength of MgO-CFB-SF was preliminarily studied. The yield stress and plastic viscosity of the MgO-CFB -SF paste were studied by rheometer. The reaction products and microstructure of MgO-CFB-SF with different ages were analyzed by XRD, TGA, FTIR and SEM. It is found the mixing of SF helps to improve the strength of the MgO-CFB-SF composites, and the composite paste with 16wt%-20wt% SF and 20wt% MgO has good flowability. The microanalysis results of MgO-CFB-SF samples maintained for 540 days at room temperature show that the main phase is magnesium silicate hydration(M-S-H), and hydrotalcite-like phase (Ht) or Al-rich magnesium silicate hydration (M-S(A)-H).
In order to make full use of the ground circulating fluidized bed combustion slag (CFB), reactive MgO, CFB and silica fume (SF) were used to prepare MgO-CFB-SF composites. The good fluidity, high strength and low cost MgO-CFB-SF composites were gained. The effects of curing temperature, SF and MgO dosage on the strength, reaction products and microstructures of MgO-CFB-SF were investigated. The effect of MgO's activity and fineness on compressive strength of MgO-CFB-SF was preliminarily studied. The yield stress and plastic viscosity of the MgO-CFB -SF paste were studied by rheometer. The reaction products and microstructure of MgO-CFB-SF with different ages were analyzed by XRD, TGA, FTIR and SEM. It is found the mixing of SF helps to improve the strength of the MgO-CFB-SF composites, and the composite paste with 16wt%-20wt% SF and 20wt% MgO has good flowability. The microanalysis results of MgO-CFB-SF samples maintained for 540 days at room temperature show that the main phase is magnesium silicate hydration(M-S-H), and hydrotalcite-like phase (Ht) or Al-rich magnesium silicate hydration (M-S(A)-H).
2018, 35(5): 1298-1305.
doi: 10.13801/j.cnki.fhclxb.20170808.005
Abstract:
According to the characteristics of sandstorm environment in central and Western Inner Mongolia, the erosion simulation system of wind-blow sand environment was utilized to study the erosion wear behavior of rubber mortar of different rubber particle size and content in sandy environment. An L16(54) Taguchi orthogonal array was adopted to design the experiment, and SEM was used to observe the micro morphology of rubber mortar after erosion. The Taguchi results show that the minimum rubber mortar erosion rate is obtained under the condition of erosion velocity of 17 m/s, rubber particle size of 1.70 mm, rubber content of 5%, impact angle of 45ånd abrasive feed rate of 45 g/min. The abrasive feed rate and erosion velocity are significant factors influencing erosion performance of rubber mortar. Under the same erosion conditions, the erosion rate of each size of the rubber mortar is as follows:1.70 mm rubber mortar < cement mortar < 0.18 mm rubber mortar < 0.42 mm rubber mortar. Rubber mortar erosion is mainly sand on the surface of the cutting and squeezing action, of which 1.70 mm rubber grain has good resistance effects on the sand, 0.42 mm powder particles is easy to spalling, which aggravate the wear of abrasive action.
According to the characteristics of sandstorm environment in central and Western Inner Mongolia, the erosion simulation system of wind-blow sand environment was utilized to study the erosion wear behavior of rubber mortar of different rubber particle size and content in sandy environment. An L16(54) Taguchi orthogonal array was adopted to design the experiment, and SEM was used to observe the micro morphology of rubber mortar after erosion. The Taguchi results show that the minimum rubber mortar erosion rate is obtained under the condition of erosion velocity of 17 m/s, rubber particle size of 1.70 mm, rubber content of 5%, impact angle of 45ånd abrasive feed rate of 45 g/min. The abrasive feed rate and erosion velocity are significant factors influencing erosion performance of rubber mortar. Under the same erosion conditions, the erosion rate of each size of the rubber mortar is as follows:1.70 mm rubber mortar < cement mortar < 0.18 mm rubber mortar < 0.42 mm rubber mortar. Rubber mortar erosion is mainly sand on the surface of the cutting and squeezing action, of which 1.70 mm rubber grain has good resistance effects on the sand, 0.42 mm powder particles is easy to spalling, which aggravate the wear of abrasive action.
2018, 35(5): 1306-1314.
doi: 10.13801/j.cnki.fhclxb.20170808.007
Abstract:
13 groups of steel fibre reinforced lightweight aggregate concrete (SFRLAC) with three kinds of strength grades were prepared. The cube compressive strength, splitting tensile strength and axial compressive strength were measured, the stress-strain curves of SFRLSC axial compression were obtained. The results show that the steel fibre can improve the compressive strength of lightweight concrete (LC) slightly, the compressive strength decreases with the increase of the haydite ratio (Vh), and the lower the strength grade is, the greater the degree decreases. Steel fibre have a significant improvement on the splitting tensile strength of LC, steel fibre on the low strength grade LC splitting tensile strength contribution is better than that of high strength grade LC. The splitting tensile strength of the low strength grade SFRLAC (LC30 and LC40) is strongly influenced by Vh, while the high strength grade SFRLAC (LC50) is opposite. When Vh reaches 80%, the Vh is no longer the main factor influencing the splitting tensile strength of SFRLAC, but the enhancement of steel fibres is remarkable. The failure of the specimen shows that steel fibre can improve the plasticity of LC. The reduction effect of the Vh on tensile strength is much greater than that of compressive strength. The relationship between axial compressive strength and cube compressive strength of SFRLAC was established. The SFRLAC stress-strain curves reflect the reinforcing effect of steel fibre and the reduction effect of haycite. The haycite decreases the peak stress and toughness of LC, while the steel fibre mainly enhances the toughness of LC.
13 groups of steel fibre reinforced lightweight aggregate concrete (SFRLAC) with three kinds of strength grades were prepared. The cube compressive strength, splitting tensile strength and axial compressive strength were measured, the stress-strain curves of SFRLSC axial compression were obtained. The results show that the steel fibre can improve the compressive strength of lightweight concrete (LC) slightly, the compressive strength decreases with the increase of the haydite ratio (Vh), and the lower the strength grade is, the greater the degree decreases. Steel fibre have a significant improvement on the splitting tensile strength of LC, steel fibre on the low strength grade LC splitting tensile strength contribution is better than that of high strength grade LC. The splitting tensile strength of the low strength grade SFRLAC (LC30 and LC40) is strongly influenced by Vh, while the high strength grade SFRLAC (LC50) is opposite. When Vh reaches 80%, the Vh is no longer the main factor influencing the splitting tensile strength of SFRLAC, but the enhancement of steel fibres is remarkable. The failure of the specimen shows that steel fibre can improve the plasticity of LC. The reduction effect of the Vh on tensile strength is much greater than that of compressive strength. The relationship between axial compressive strength and cube compressive strength of SFRLAC was established. The SFRLAC stress-strain curves reflect the reinforcing effect of steel fibre and the reduction effect of haycite. The haycite decreases the peak stress and toughness of LC, while the steel fibre mainly enhances the toughness of LC.
2018, 35(5): 1315-1324.
doi: 10.13801/j.cnki.fhclxb.20171128.001
Abstract:
In order to provide reference for the design and construction of reinforced concrete columns strengthened with fiber reinforced polymer composite(FRP) under corrosive environment, and to promote its application, the accelerated corrosion was conducted to get the damaged reinforced concrete column which was similar to the action of actual environment. Then, the carbon fiber reinforced polymer composite(CFRP) strips and glass fiber reinforced polymer composite (GFRP) strips were used to strengthen the corroded reinforced concrete columns respectively. Finally, the axial compression tests were carried out on the corroded reinforced concrete columns strengthened with FRP to investigate the effect of rebar corrosion rate, FRP layers and types on the compressive bearing capacity of columns. Based on the research and analysis of the action effect of FRP with interval constraints, rebar corrosion on concrete section and mechanical properties of corroded reinforcement, the calculation model of the axial compressive bearing capacity of corroded reinforced concrete columns strengthened with FRP was presented. The average value of the ratios of measured compressive bearing capacity to calculated by the model is 1.020, and the coefficient of variation is 0.063, which indicates that the calculation model is in good agreement with the test reslts.
In order to provide reference for the design and construction of reinforced concrete columns strengthened with fiber reinforced polymer composite(FRP) under corrosive environment, and to promote its application, the accelerated corrosion was conducted to get the damaged reinforced concrete column which was similar to the action of actual environment. Then, the carbon fiber reinforced polymer composite(CFRP) strips and glass fiber reinforced polymer composite (GFRP) strips were used to strengthen the corroded reinforced concrete columns respectively. Finally, the axial compression tests were carried out on the corroded reinforced concrete columns strengthened with FRP to investigate the effect of rebar corrosion rate, FRP layers and types on the compressive bearing capacity of columns. Based on the research and analysis of the action effect of FRP with interval constraints, rebar corrosion on concrete section and mechanical properties of corroded reinforcement, the calculation model of the axial compressive bearing capacity of corroded reinforced concrete columns strengthened with FRP was presented. The average value of the ratios of measured compressive bearing capacity to calculated by the model is 1.020, and the coefficient of variation is 0.063, which indicates that the calculation model is in good agreement with the test reslts.
2018, 35(5): 1325-1331.
doi: 10.13801/j.cnki.fhclxb.20170802.002
Abstract:
The surface displacement field and strain field of steel fiber reinforced cement matrix composites at three-point bending falling ball impact test were calculated and studied by the digital image correlation (DIC) technology. The impact times of initial crack was determined by the displacement near the crack point. And the whole horizontal strain was statistically analyzed to obtain damage factor(Df) characterization curve under impact. The influence law of bending impact damage with different fiber dosage was further investigated. The experimental results indicate that compared with the effect to the initial crack impact times, the steel fibers effect to the crack impact times is more obvious; Df curve can better reflect the impact of shock load and the bending impact of the specimen is destroyed, based on the damage factor characterization curve, the impact bending process has tardiness, acceleration and tardiness stages; The more fiber content, the slower Df curve development, the greater the proportion of the tardiness stage of the three impact damage stages. And steel fiber toughening effect mainly displays in the tardiness stage.
The surface displacement field and strain field of steel fiber reinforced cement matrix composites at three-point bending falling ball impact test were calculated and studied by the digital image correlation (DIC) technology. The impact times of initial crack was determined by the displacement near the crack point. And the whole horizontal strain was statistically analyzed to obtain damage factor(Df) characterization curve under impact. The influence law of bending impact damage with different fiber dosage was further investigated. The experimental results indicate that compared with the effect to the initial crack impact times, the steel fibers effect to the crack impact times is more obvious; Df curve can better reflect the impact of shock load and the bending impact of the specimen is destroyed, based on the damage factor characterization curve, the impact bending process has tardiness, acceleration and tardiness stages; The more fiber content, the slower Df curve development, the greater the proportion of the tardiness stage of the three impact damage stages. And steel fiber toughening effect mainly displays in the tardiness stage.
2018, 35(5): 1332-1338.
doi: 10.13801/j.cnki.fhclxb.20170702.003
Abstract:
Because of the poor interaction between carbon nanotubes(CNTs) and Pt nanoparticles in CNTs-supported Pt catalyst, the electrical conductivity between them is poor and the Pt nanoparticles may fall off or agglomerate. In this paper, the adsorption of Pt atom at different sites of the CNTs cap was investigated using the first principles theory. It is found that the average adsorption energy between (5,5) CNTs-Pt and (9,0) CNTs-Pt at different sites can be increased respectively by 12.7% and 19.6% by doping B, and 22.4% and 18.4% by doping N. The charge transfer between CNTs and Pt can also be significantly elevated compared with Pt adsorption at the tube side. In addition, the stability of the CNTs-Pt system can be increased by up to 133.8% (B-doping) and 237.3% (N-doping). The research indicates that doping B or N at the CNTs end can both improve the efficiency of CNTs-supported Pt catalyst.
Because of the poor interaction between carbon nanotubes(CNTs) and Pt nanoparticles in CNTs-supported Pt catalyst, the electrical conductivity between them is poor and the Pt nanoparticles may fall off or agglomerate. In this paper, the adsorption of Pt atom at different sites of the CNTs cap was investigated using the first principles theory. It is found that the average adsorption energy between (5,5) CNTs-Pt and (9,0) CNTs-Pt at different sites can be increased respectively by 12.7% and 19.6% by doping B, and 22.4% and 18.4% by doping N. The charge transfer between CNTs and Pt can also be significantly elevated compared with Pt adsorption at the tube side. In addition, the stability of the CNTs-Pt system can be increased by up to 133.8% (B-doping) and 237.3% (N-doping). The research indicates that doping B or N at the CNTs end can both improve the efficiency of CNTs-supported Pt catalyst.
2018, 35(5): 1339-1348.
doi: 10.13801/j.cnki.fhclxb.20170704.003
Abstract:
The mechanical properties and the fractions of individual phases at microscale were measured by nanoindentation and back scattered electron (BSE) image analysis, and they can be used as the input in modeling the mechanical properties of cement paste. The mechanical properties of cement paste were measured by microindentation. The effect of individual phases on the effective modulus of hardened cement paste was quantified by comparing the measured and homogenized paste modulus. It is found that the effective modulus of pore needs to be set to 12 GPa as input for homogenization. Meanwhile, the high density hydrated calcium silicate gel (HD-CSH) and the low density hydrated calcium silicate gel (LD-CSH) need to be viewed as two different phases in modeling. Whereas, different clinkers can be regarded a single phase. The effective paste moduli calculated by both Mori-Tanaka scheme and self-consistent scheme agree well with the measured paste modulus.
The mechanical properties and the fractions of individual phases at microscale were measured by nanoindentation and back scattered electron (BSE) image analysis, and they can be used as the input in modeling the mechanical properties of cement paste. The mechanical properties of cement paste were measured by microindentation. The effect of individual phases on the effective modulus of hardened cement paste was quantified by comparing the measured and homogenized paste modulus. It is found that the effective modulus of pore needs to be set to 12 GPa as input for homogenization. Meanwhile, the high density hydrated calcium silicate gel (HD-CSH) and the low density hydrated calcium silicate gel (LD-CSH) need to be viewed as two different phases in modeling. Whereas, different clinkers can be regarded a single phase. The effective paste moduli calculated by both Mori-Tanaka scheme and self-consistent scheme agree well with the measured paste modulus.
2018, 35(5): 1349-1353.
doi: 10.13801/j.cnki.fhclxb.20170707.002
Abstract:
On the basis of the four point bending experiments of beams and slabs of hybrid fiber reinforced cementitious composites with CaCO3 whisker, a mathematical formula was proposed to determine the relationship between flexural toughness index and fiber reinforcing index (S). The S takes into account of the effect of the fiber tensile strength and mechanical anchorage on the flexural tensile properties of hybrid fiber/concrete, which has clear physical meaning. The quadratic function can reflect the toughness reinforcing effect of hybrid fiber system on the hybrid fiber/concrete, and it can be used to optimize fiber composition by determining the extreme value of the quadratic function. The mathematical model has good applicability on steel-synthetic and steel-plant fibers reinforced concrete, without considering the matrix (mortar or concrete) and specimen shape (beam or slab). In addition, the formula can be applied not only to the flexural toughness and equivalent flexural strength, but also to the flexural toughness index based on ASTM C1018, e.g. I5, I10, I30 and I50.
On the basis of the four point bending experiments of beams and slabs of hybrid fiber reinforced cementitious composites with CaCO3 whisker, a mathematical formula was proposed to determine the relationship between flexural toughness index and fiber reinforcing index (S). The S takes into account of the effect of the fiber tensile strength and mechanical anchorage on the flexural tensile properties of hybrid fiber/concrete, which has clear physical meaning. The quadratic function can reflect the toughness reinforcing effect of hybrid fiber system on the hybrid fiber/concrete, and it can be used to optimize fiber composition by determining the extreme value of the quadratic function. The mathematical model has good applicability on steel-synthetic and steel-plant fibers reinforced concrete, without considering the matrix (mortar or concrete) and specimen shape (beam or slab). In addition, the formula can be applied not only to the flexural toughness and equivalent flexural strength, but also to the flexural toughness index based on ASTM C1018, e.g. I5, I10, I30 and I50.
2018, 35(5): 1354-1360.
doi: 10.13801/j.cnki.fhclxb.20170807.001
Abstract:
The extended finite element method(XFEM) and cohesive zone model(CZM) were combined to investigate the adhesive layer of scarf-repaired laminates, which could describe the debonding between composite and adhesive layer and the crack propagation in the adhesive at the same time. The numerical strength shows good agreement with test results. Both the interface defect and inner defect were taken into consideration, the influences of defect length and defect location were analyzed. The results indicate that the structure with inner defect is more dangerous than that with interface defect under the same condition. The structure strength which is influenced by both the defect length and the ply orientation near the defect tip decreases with the increased defect length. And the decrease rate is larger than the increase rate of defect length. When the defect location changes, the structure strength is mainly associated with the average shear stress level of adhesive layer at corresponding region. At last, parameter study was performed to investigate the influence of the interface shear strength.
The extended finite element method(XFEM) and cohesive zone model(CZM) were combined to investigate the adhesive layer of scarf-repaired laminates, which could describe the debonding between composite and adhesive layer and the crack propagation in the adhesive at the same time. The numerical strength shows good agreement with test results. Both the interface defect and inner defect were taken into consideration, the influences of defect length and defect location were analyzed. The results indicate that the structure with inner defect is more dangerous than that with interface defect under the same condition. The structure strength which is influenced by both the defect length and the ply orientation near the defect tip decreases with the increased defect length. And the decrease rate is larger than the increase rate of defect length. When the defect location changes, the structure strength is mainly associated with the average shear stress level of adhesive layer at corresponding region. At last, parameter study was performed to investigate the influence of the interface shear strength.
