2010 Vol. 27, No. 3
2010, 27(3): 1-9.
Abstract:
Research findings of the forewing structure of beetles and the development prospects of biomimetic applications were reviewed in this paper. The forewing is of frame structure with small columns as void lamination,and the coupling area of the left and right forewings is of the concave-convex meshing structure. The honeycomb-columniation structure , which exists in the forewing, is a kind of lightweight sandwich plate structure. The fibersbetween the columniation and the upper and lower layers of laminated composite material are continuous , which could effectively enhance the anti-stripping strength of the laminated composite materials. Special biological structures exist in the forewing surface of some beetles , leading to its special properties, such as drag-reduction, water capturing, and color development. A novel idea for producing biomimetic materials was proposed by designing vital genes.
Research findings of the forewing structure of beetles and the development prospects of biomimetic applications were reviewed in this paper. The forewing is of frame structure with small columns as void lamination,and the coupling area of the left and right forewings is of the concave-convex meshing structure. The honeycomb-columniation structure , which exists in the forewing, is a kind of lightweight sandwich plate structure. The fibersbetween the columniation and the upper and lower layers of laminated composite material are continuous , which could effectively enhance the anti-stripping strength of the laminated composite materials. Special biological structures exist in the forewing surface of some beetles , leading to its special properties, such as drag-reduction, water capturing, and color development. A novel idea for producing biomimetic materials was proposed by designing vital genes.
2010, 27(3): 10-15.
Abstract:
Multi-walled carbon nanotubes (MWCNTs) reinforced poly(ε-caprolactone) (PCL) ult rafine composite fibers were prepared by means of elect rospinning. Scanning electron microscopy (SEM) , transmission electron microscopy (TEM), Raman spect roscopy, differential scanning calorimeter (DSC) and X-ray diff raction (XRD) were used to characterize the electrospun ultrafine MWCNTs/PCL fibers and the mechanical properties of fibers were also tested. The results indicate that MWCNTs have been dispersed in PCL, which can reduce the crystallization of PCL. When the content of MWCNTs is 0. 5 wt% , elect rospun MWCNTs/PCL composite fibers have the best mechanical properties with the lowest crystallinity of PCL.
Multi-walled carbon nanotubes (MWCNTs) reinforced poly(ε-caprolactone) (PCL) ult rafine composite fibers were prepared by means of elect rospinning. Scanning electron microscopy (SEM) , transmission electron microscopy (TEM), Raman spect roscopy, differential scanning calorimeter (DSC) and X-ray diff raction (XRD) were used to characterize the electrospun ultrafine MWCNTs/PCL fibers and the mechanical properties of fibers were also tested. The results indicate that MWCNTs have been dispersed in PCL, which can reduce the crystallization of PCL. When the content of MWCNTs is 0. 5 wt% , elect rospun MWCNTs/PCL composite fibers have the best mechanical properties with the lowest crystallinity of PCL.
2010, 27(3): 16-21.
Abstract:
Multiwall carbon nanotubes (MWCNTs) were modified by mixed acid and tet rafluoro carbon (CF4 ) plasma treatment. The surface morphology and structure of MWCNTs before and after treatment were obtained by using SEM and XPS, which revealed that MWCNTs can be grafted by polar groups after surface treatment. Furthermore, MWCNTs/fluoro-elastomer ( FE) composite films were prepared by the method of solution casting using untreated MWCNTs (UCNTs) , acid-modified MWCNTs (ACNTs) and CF4 plasma-modified MWCNTs (FCNTs). In each case, MWCNTs mass fractions were 0. 1 % , 0. 5 %, 1. 0 % and 2. 0 % with respect to the polymer. The conductivity of MWCNTs/FE was studied by comparing the modification effect on MWCNTs. The results show that the lowest percolation threshold in acid-modified MWCNTs/FE composites was about 0. 5 %.
Multiwall carbon nanotubes (MWCNTs) were modified by mixed acid and tet rafluoro carbon (CF4 ) plasma treatment. The surface morphology and structure of MWCNTs before and after treatment were obtained by using SEM and XPS, which revealed that MWCNTs can be grafted by polar groups after surface treatment. Furthermore, MWCNTs/fluoro-elastomer ( FE) composite films were prepared by the method of solution casting using untreated MWCNTs (UCNTs) , acid-modified MWCNTs (ACNTs) and CF4 plasma-modified MWCNTs (FCNTs). In each case, MWCNTs mass fractions were 0. 1 % , 0. 5 %, 1. 0 % and 2. 0 % with respect to the polymer. The conductivity of MWCNTs/FE was studied by comparing the modification effect on MWCNTs. The results show that the lowest percolation threshold in acid-modified MWCNTs/FE composites was about 0. 5 %.
2010, 27(3): 22-28.
Abstract:
To obtain good dispersion and interface characteristics in epoxy resin ( EP) composites, carbon nanotubes (CNTs) were firstly hydroxylated with Fenton reagent treatment, and then surface-modified with silane coupling agent KH550, KH560, KH570 and titanate coupling agent NDZ2201, respectively. The influence of coupling agent modification on the properties of CNTs/EP composites was investigated by SEM, DSC, TGA and impedance analyzer. The experimental results show that Fenton reagent treatment and modification using four kinds of coupling agents can all obviously improve the dispersion of CNTs, glass transition temperature (Tg) and thermal stability of EP. All coupling agent modifications are more effective than the Fenton reagent treatment. However, these modifications can significantly reduce the electric conductivity, permittivity and dielectric loss of the composites. Among the four kinds of coupling agent modification, the composite modified by KH560 shows the highest Tg, the best thermal stability and electric conductivity, high permittivity and low dielectric loss.
To obtain good dispersion and interface characteristics in epoxy resin ( EP) composites, carbon nanotubes (CNTs) were firstly hydroxylated with Fenton reagent treatment, and then surface-modified with silane coupling agent KH550, KH560, KH570 and titanate coupling agent NDZ2201, respectively. The influence of coupling agent modification on the properties of CNTs/EP composites was investigated by SEM, DSC, TGA and impedance analyzer. The experimental results show that Fenton reagent treatment and modification using four kinds of coupling agents can all obviously improve the dispersion of CNTs, glass transition temperature (Tg) and thermal stability of EP. All coupling agent modifications are more effective than the Fenton reagent treatment. However, these modifications can significantly reduce the electric conductivity, permittivity and dielectric loss of the composites. Among the four kinds of coupling agent modification, the composite modified by KH560 shows the highest Tg, the best thermal stability and electric conductivity, high permittivity and low dielectric loss.
2010, 27(3): 29-35.
Abstract:
SiO2/polyacrylate composite emulsions ( Si/PAE) were prepared by polyacrylate emulsions (PAE) mixing with alkaline silica sol modified by a saline coupling agent and a co-solvent. The effects of kinds and amounts of co-solvent s on the sol-gel reaction and the properties of composite films were investigated. The results indicate that isopropanol is the best co-solvent and the optimal dosage is 10 wt% of the silica sol. The nano-granularity analysis and TEM photos show that co-solvents can make the silica particles distribute more evenly in the composite emulsions and reduce the average diameters of the Si/PAE. The FTIR spectra and AFM pictures indicate that co-solvents could induce the occurrence of sol-gel reaction of silica sol to form Si-based polymers on the surface of films during the film formation. Si/ PAE films display excellent properties besides high gloss and compact. TGA curves indicate that the Si/PAE films exhibit higher thermal stability than PAE.
SiO2/polyacrylate composite emulsions ( Si/PAE) were prepared by polyacrylate emulsions (PAE) mixing with alkaline silica sol modified by a saline coupling agent and a co-solvent. The effects of kinds and amounts of co-solvent s on the sol-gel reaction and the properties of composite films were investigated. The results indicate that isopropanol is the best co-solvent and the optimal dosage is 10 wt% of the silica sol. The nano-granularity analysis and TEM photos show that co-solvents can make the silica particles distribute more evenly in the composite emulsions and reduce the average diameters of the Si/PAE. The FTIR spectra and AFM pictures indicate that co-solvents could induce the occurrence of sol-gel reaction of silica sol to form Si-based polymers on the surface of films during the film formation. Si/ PAE films display excellent properties besides high gloss and compact. TGA curves indicate that the Si/PAE films exhibit higher thermal stability than PAE.
2010, 27(3): 36-42.
Abstract:
The organic nano-montmorillonite (OMMT) /poly ( styrene-co-divinylbenzene , St ) composites were prepared by suspension polymerization. OMMT was prepared by the ionexchange method between sodium montmorillonite (SMMT) and cetylt rimethyl ammonium bromide (CTAB) in an aqueous solution. The character and structure of OMMT were revealed by XRD and FTIR. The microstructure of composites was characterized by XRD, TEM, SEM and FTIR. The thermal stability of composites was studied by TG. The effect of the amount of OMMT and divinylbenzene (DVB) on the thermal stability of composites was discussed. The results indicate that the maximum interlayer spacing is 1. 48 nm for SMMT, 2. 85 nm for OMMT and about 4. 0 nm for OMMT/polymer. The maximum decomposed temperatures are 399 ℃ for the pure polystyrene and 437 ℃ for composites with montmorillonite mass f raction of 5 % and DVB content of 10 %. The crosslinked composites exhibit drastic improvements in hermal stability under the experimental conditions.
The organic nano-montmorillonite (OMMT) /poly ( styrene-co-divinylbenzene , St ) composites were prepared by suspension polymerization. OMMT was prepared by the ionexchange method between sodium montmorillonite (SMMT) and cetylt rimethyl ammonium bromide (CTAB) in an aqueous solution. The character and structure of OMMT were revealed by XRD and FTIR. The microstructure of composites was characterized by XRD, TEM, SEM and FTIR. The thermal stability of composites was studied by TG. The effect of the amount of OMMT and divinylbenzene (DVB) on the thermal stability of composites was discussed. The results indicate that the maximum interlayer spacing is 1. 48 nm for SMMT, 2. 85 nm for OMMT and about 4. 0 nm for OMMT/polymer. The maximum decomposed temperatures are 399 ℃ for the pure polystyrene and 437 ℃ for composites with montmorillonite mass f raction of 5 % and DVB content of 10 %. The crosslinked composites exhibit drastic improvements in hermal stability under the experimental conditions.
2010, 27(3): 43-49.
Abstract:
To use heat pipe cooled thermal protection structure (TPS) is a noval efficient thermal protection method. A model of the heat pipe cooled C/C composite TPS was established herein, where the assembly relationship of the C/C composite material and the heat pipe was int roduced by the penalty method, and a finite element algorithm of the thermomechanical analysis by using the sequential coupling method was also developed. Based on the numerical method, the thermomechanical coupling and parametric analysis had been implemented. The numerical results show that, under the typical flying condition, the heat pipe cooled C/C composite TPS can make sure that the stagnation temperature is in the tolerance zone. The contact stress can be greatly reduced by allocating initial gap between the heat pipe and the thermal structure. The present method can also be used to investigate the thermomechanical coupling problems caused by thermal contact resistance.
To use heat pipe cooled thermal protection structure (TPS) is a noval efficient thermal protection method. A model of the heat pipe cooled C/C composite TPS was established herein, where the assembly relationship of the C/C composite material and the heat pipe was int roduced by the penalty method, and a finite element algorithm of the thermomechanical analysis by using the sequential coupling method was also developed. Based on the numerical method, the thermomechanical coupling and parametric analysis had been implemented. The numerical results show that, under the typical flying condition, the heat pipe cooled C/C composite TPS can make sure that the stagnation temperature is in the tolerance zone. The contact stress can be greatly reduced by allocating initial gap between the heat pipe and the thermal structure. The present method can also be used to investigate the thermomechanical coupling problems caused by thermal contact resistance.
2010, 27(3): 50-55.
Abstract:
The anti-oxidation coatings of SiC/ZrB2-MoSi2 on the carbon/ carbon composites were prepared by pack cementation and slurry painting. The coating microstructure, performance and the anti-oxidation mechanisms were investigated by SEM, XRD, etc. The results show that the inner coating of SiC can eliminate the thermal expansion mismatch between carbon/carbon composites and the outer coating of ZrB2-MoSi2. The coating mass loss of ZrB2-MoSi2 prepared by slurry painting with a lot of craze cracks is 3.58 % after 10 h in air at 1500 ℃. The coating exhibits self-healing performance, excellent anti-oxidation ability and thermal shock resistance.
The anti-oxidation coatings of SiC/ZrB2-MoSi2 on the carbon/ carbon composites were prepared by pack cementation and slurry painting. The coating microstructure, performance and the anti-oxidation mechanisms were investigated by SEM, XRD, etc. The results show that the inner coating of SiC can eliminate the thermal expansion mismatch between carbon/carbon composites and the outer coating of ZrB2-MoSi2. The coating mass loss of ZrB2-MoSi2 prepared by slurry painting with a lot of craze cracks is 3.58 % after 10 h in air at 1500 ℃. The coating exhibits self-healing performance, excellent anti-oxidation ability and thermal shock resistance.
2010, 27(3): 56-60.
Abstract:
La-doped Ca manganese oxide powders ((La1- x Cax Mn0. 7Co0. 3O3, x = 1. 0, 0. 9, 0. 8 , 0. 7, 0.6) and their polypyrrole compositesLa0. 3Ca0.7Mn0. 7Co0. 3O3/PPy with 60 % and 80 % PPy were prepared by a glycine-nit rate combustion method and an as-polymerization method, respectively. The structure, morphologies and electrochemical properties of the samples were characterized by means of Fourier transform inf rared (FTIR) spectrometer, powder X-ray diff ractometer (XRD), scanning electron microscope (SEM) and electrochemical tests. The results indicate that interactions exist between polypyrrole and complex oxide. Furthermore, PPy reduces the reunion of the nano2particles, i. e. the particle sizes ofLa0. 3Ca0.7Mn0. 7Co0. 3O3 andLa0. 3Ca0.7Mn0. 7Co0. 3O3/PPy are 46. 2 nm and 43. 5 nm, respectively. The composite redox peak current becomes larger with increasing of pyrrole contents.
La-doped Ca manganese oxide powders ((La1- x Cax Mn0. 7Co0. 3O3, x = 1. 0, 0. 9, 0. 8 , 0. 7, 0.6) and their polypyrrole compositesLa0. 3Ca0.7Mn0. 7Co0. 3O3/PPy with 60 % and 80 % PPy were prepared by a glycine-nit rate combustion method and an as-polymerization method, respectively. The structure, morphologies and electrochemical properties of the samples were characterized by means of Fourier transform inf rared (FTIR) spectrometer, powder X-ray diff ractometer (XRD), scanning electron microscope (SEM) and electrochemical tests. The results indicate that interactions exist between polypyrrole and complex oxide. Furthermore, PPy reduces the reunion of the nano2particles, i. e. the particle sizes ofLa0. 3Ca0.7Mn0. 7Co0. 3O3 andLa0. 3Ca0.7Mn0. 7Co0. 3O3/PPy are 46. 2 nm and 43. 5 nm, respectively. The composite redox peak current becomes larger with increasing of pyrrole contents.
2010, 27(3): 61-66.
Abstract:
Aliphatic polyurethanes based on 4, 4′-dicyclohexylmethane diisocyanate ( H12MDI), poly ( ethylene glycol) (PEG), castor oil (CO), 1, 4-butandiol (BDO) and bioactive nano-hydroxyapatite (n-HA) were selected to prepare a nanocomposite by the prepolymerization method. The mechanical and thermal properties of the nano-composites were investigated. The results show that the tensile strength and broken elongation of the nano-composites are all reinforced with the addition of nano HA particles. When incorporation of 30 wt% n-HA into PU matrix, the tensile st rength and broken elongation increase by 186 % and 107 % compared to those of pure PU, respectively, which reach the maximum values. The storage modulus of the composites increases obviously with the increase of n-HA loading. The nano composites exhibit improved thermal stability with the incorporation of HA nanoparticles, and the differential scanning calorimetry (DSC) indicates that the incorporation of n-HA can hinder the crystallization process of PU. These results suggest that the n-HA/PU composite might be a prospective material for future applications in tissue engineering.
Aliphatic polyurethanes based on 4, 4′-dicyclohexylmethane diisocyanate ( H12MDI), poly ( ethylene glycol) (PEG), castor oil (CO), 1, 4-butandiol (BDO) and bioactive nano-hydroxyapatite (n-HA) were selected to prepare a nanocomposite by the prepolymerization method. The mechanical and thermal properties of the nano-composites were investigated. The results show that the tensile strength and broken elongation of the nano-composites are all reinforced with the addition of nano HA particles. When incorporation of 30 wt% n-HA into PU matrix, the tensile st rength and broken elongation increase by 186 % and 107 % compared to those of pure PU, respectively, which reach the maximum values. The storage modulus of the composites increases obviously with the increase of n-HA loading. The nano composites exhibit improved thermal stability with the incorporation of HA nanoparticles, and the differential scanning calorimetry (DSC) indicates that the incorporation of n-HA can hinder the crystallization process of PU. These results suggest that the n-HA/PU composite might be a prospective material for future applications in tissue engineering.
2010, 27(3): 67-72.
Abstract:
The toughening and reinforcement mechanism of HA ( hydroxyapatite ) /HDPE ( high density polyethylene ) composite was investigated. The results show that the co-operative actions of multi-scale is the main role to enhance the mechanical properties. On the nano-scale, the homogeneous dispersion of HA and high interfacial strength between HA and HDPE leads to the high crystalline, litter crystal size and the formation of oriented extended-chain crystal structure. This will result in the HDPE deformation and HA deadhesion during the fracture process, which can pin the development of microcracks, expend large energies and prohibit the formation of large crack. On the micro-scale, the formation of oriented HA/HDPE fibers can greatly reduce the activity volume and increase the fracture energy, which leads to the high st rength. On the other hand, the composite fiber can expend much more energy by fracture, pullout and crackbowing, which enhances the strength and toughness to a great extent.
The toughening and reinforcement mechanism of HA ( hydroxyapatite ) /HDPE ( high density polyethylene ) composite was investigated. The results show that the co-operative actions of multi-scale is the main role to enhance the mechanical properties. On the nano-scale, the homogeneous dispersion of HA and high interfacial strength between HA and HDPE leads to the high crystalline, litter crystal size and the formation of oriented extended-chain crystal structure. This will result in the HDPE deformation and HA deadhesion during the fracture process, which can pin the development of microcracks, expend large energies and prohibit the formation of large crack. On the micro-scale, the formation of oriented HA/HDPE fibers can greatly reduce the activity volume and increase the fracture energy, which leads to the high st rength. On the other hand, the composite fiber can expend much more energy by fracture, pullout and crackbowing, which enhances the strength and toughness to a great extent.
2010, 27(3): 73-77.
Abstract:
A macroporous calcium phosphate cement (CPC) scaffold with oriented pore structure was prepared by the unidirectional freeze casting method. Two kinds of poly ( lactic-co-glycolic acid) ( PLGA) with different degradation rates were infiltrated into the CPC scaffold to improve the mechanical strength. The results indicate that the compressive strength of scaffolds is greatly improved via PLGA reinforcement. The compressive strength of 6. 37 MPa ±0. 54 MPa is achieved for the PLGA/CPC scaffold. The PLGA/CPC scaffolds prepared by infiltration with PLGA still possess open oriented pore structure, which would be helpful for bone ingrowth into the implant. The PLGA membrane coat on the pore walls of the CPC scaffold can strengthen the matrix and remedy the defects. PLGA sponges in the scaffold can participate in bearing the external load. These contribute to the high strength and toughness of the composite scaffold.
A macroporous calcium phosphate cement (CPC) scaffold with oriented pore structure was prepared by the unidirectional freeze casting method. Two kinds of poly ( lactic-co-glycolic acid) ( PLGA) with different degradation rates were infiltrated into the CPC scaffold to improve the mechanical strength. The results indicate that the compressive strength of scaffolds is greatly improved via PLGA reinforcement. The compressive strength of 6. 37 MPa ±0. 54 MPa is achieved for the PLGA/CPC scaffold. The PLGA/CPC scaffolds prepared by infiltration with PLGA still possess open oriented pore structure, which would be helpful for bone ingrowth into the implant. The PLGA membrane coat on the pore walls of the CPC scaffold can strengthen the matrix and remedy the defects. PLGA sponges in the scaffold can participate in bearing the external load. These contribute to the high strength and toughness of the composite scaffold.
2010, 27(3): 78-85.
Abstract:
A new method is developed for building a relationship among the viscosity, temperature, curing degree and time to predict the viscosity of the reactive resin system which is affected by the cure degree, temperature and ejective heat of the cure reaction. This method, starting with isothermal viscosity-time curves and isothermal curing degree-time curves, and separates of the curing degree and the temperature effect in the real environment, which were two main factors affecting the reactive resin viscosity. Based on the assumption that the reactive resin system is a partial adiabatic system, the viscosity-time relationship of a reactive resin system under the combined influences of curing degree, temperature and ejective heat of the cure reaction was rebuilt. The viscosity prediction has the high consistency with the test values using the rolling viscometer. The new method can be used to predict the viscosity of the reactive resin system in considering the ejective heat of the cure reaction.
A new method is developed for building a relationship among the viscosity, temperature, curing degree and time to predict the viscosity of the reactive resin system which is affected by the cure degree, temperature and ejective heat of the cure reaction. This method, starting with isothermal viscosity-time curves and isothermal curing degree-time curves, and separates of the curing degree and the temperature effect in the real environment, which were two main factors affecting the reactive resin viscosity. Based on the assumption that the reactive resin system is a partial adiabatic system, the viscosity-time relationship of a reactive resin system under the combined influences of curing degree, temperature and ejective heat of the cure reaction was rebuilt. The viscosity prediction has the high consistency with the test values using the rolling viscometer. The new method can be used to predict the viscosity of the reactive resin system in considering the ejective heat of the cure reaction.
2010, 27(3): 86-91.
Abstract:
An experimental investigation was carried out to deal with the unmatched problem between the gel-time and full-time in vacuum infusion process (VIP). By studying the thickness change of process part s prepared by VIP in different layers, an empirical formula related with resin flow distance, fiber layersp numbers and thickness was obtained and the feasibility of this formula was validated. Problems and defects existing in the practical process were analyzed and the improved experimental methods were also discussed to improve the process efficiency and products' quality in engineering.
An experimental investigation was carried out to deal with the unmatched problem between the gel-time and full-time in vacuum infusion process (VIP). By studying the thickness change of process part s prepared by VIP in different layers, an empirical formula related with resin flow distance, fiber layersp numbers and thickness was obtained and the feasibility of this formula was validated. Problems and defects existing in the practical process were analyzed and the improved experimental methods were also discussed to improve the process efficiency and products' quality in engineering.
2010, 27(3): 92-98.
Abstract:
The glass fiber reinforced epoxy resin polymer (GFRP) laminates with thickness of 85 mm were manufactured by the vacuum infusion molding process (VIMP), cured by one-side rigid mould heating. The temperature curves at different thickness positions during curing were examined, which shows large temperature changes in the thickness direction. The curing kinetics of the epoxy resin system was studied under isothermal curing conditions by differential scanning calorimetry (DSC) technique. The cure kinetic equations based on the autocatalytic kinetic model were established and were verified by the experimental data. A method of accumulation by time dispersing steps was set up and used to calculate the dist ribution of the degree of cure curves at different thickness positions in the curing course. The results show that there were large differences of real time degree of cure in pre-curing process, but the high equivalent degree of cure could be achieved by the post-curing process. This method could be used to calculate the asymmetrical distribution of the degree of cure in the curing course and optimize the curing stage.
The glass fiber reinforced epoxy resin polymer (GFRP) laminates with thickness of 85 mm were manufactured by the vacuum infusion molding process (VIMP), cured by one-side rigid mould heating. The temperature curves at different thickness positions during curing were examined, which shows large temperature changes in the thickness direction. The curing kinetics of the epoxy resin system was studied under isothermal curing conditions by differential scanning calorimetry (DSC) technique. The cure kinetic equations based on the autocatalytic kinetic model were established and were verified by the experimental data. A method of accumulation by time dispersing steps was set up and used to calculate the dist ribution of the degree of cure curves at different thickness positions in the curing course. The results show that there were large differences of real time degree of cure in pre-curing process, but the high equivalent degree of cure could be achieved by the post-curing process. This method could be used to calculate the asymmetrical distribution of the degree of cure in the curing course and optimize the curing stage.
2010, 27(3): 99-104.
Abstract:
Wheat straw fiber-polypropylene ( PP) composites were prepared by means of the extrusion and moulded pressing process. The effects of the wheat straw fiber content, fiber size, MAPP concentration, and temperature on the melt rheological properties of PP composites were investigated. Adding wheat straw fiber to polymer matrix can increase the melt viscosity of the PP composites. The introduction of MAPP to the system increases the flow behavior of polymer and decreases the melt viscosity. The longer the wheat straw fibers, the lower the melt viscosity, and the finer the wheat straw fibers, the higher the melt viscosity. The melt viscosity of the PP composites decreases with increasing temperature f rom 170 ℃ to 190 ℃, and increasing shear rate from 0. 01 to 0. 1 s -1.
Wheat straw fiber-polypropylene ( PP) composites were prepared by means of the extrusion and moulded pressing process. The effects of the wheat straw fiber content, fiber size, MAPP concentration, and temperature on the melt rheological properties of PP composites were investigated. Adding wheat straw fiber to polymer matrix can increase the melt viscosity of the PP composites. The introduction of MAPP to the system increases the flow behavior of polymer and decreases the melt viscosity. The longer the wheat straw fibers, the lower the melt viscosity, and the finer the wheat straw fibers, the higher the melt viscosity. The melt viscosity of the PP composites decreases with increasing temperature f rom 170 ℃ to 190 ℃, and increasing shear rate from 0. 01 to 0. 1 s -1.
2010, 27(3): 105-110.
Abstract:
In order to improve accuracy and real-time of impact localization in composite, the array signal processing technique was introduced into the area of structure health monitoring and a new method for impact monitoring in composite was proposed based on the wavelet transform and multiple signal classification (MUSIC) method. Firstly, narrowband frequency components of response signals were extracted by using wavelet transform, followed by the estimation of the direction-of-arrival (DOA) based on MUSIC method. Secondly, based on the propagation characteristics of lamb wave, the time-delay between symmetry and antisymmetry modal waves of one central frequency lamb wave arriving to the same array element was gained by using the wavelet transform, and the distance between impact source and array element was estimated according to velocity difference between symmetry and antisymmetry modal waves, thus the impact localization was realized. Experiments on the laminated glass fiber reinforced epoxy composite and laminated carbon fiber reinforced bismaleimide composite indicate that the present methodology can identify the impact location fast and accurately.
In order to improve accuracy and real-time of impact localization in composite, the array signal processing technique was introduced into the area of structure health monitoring and a new method for impact monitoring in composite was proposed based on the wavelet transform and multiple signal classification (MUSIC) method. Firstly, narrowband frequency components of response signals were extracted by using wavelet transform, followed by the estimation of the direction-of-arrival (DOA) based on MUSIC method. Secondly, based on the propagation characteristics of lamb wave, the time-delay between symmetry and antisymmetry modal waves of one central frequency lamb wave arriving to the same array element was gained by using the wavelet transform, and the distance between impact source and array element was estimated according to velocity difference between symmetry and antisymmetry modal waves, thus the impact localization was realized. Experiments on the laminated glass fiber reinforced epoxy composite and laminated carbon fiber reinforced bismaleimide composite indicate that the present methodology can identify the impact location fast and accurately.
2010, 27(3): 111-115.
Abstract:
A smart layer was developed by effectively overlapping continuous carbon fibers in a local area in epoxy matrix. The smart layer was stuck on the st ructure surface to sense its deformation and perform a large-region monitoring. Based on the smart layer, the strain and displacement of the components were detected in the uniaxial tension and three-point bending experiments. The results indicate that the local overlapped structure is the essence of the overlapped carbon fiber polymer-matrix smart layer. The gauge factor of the overlapped carbon fiber polymer-matrix smart layer, defined as fractional change in resistance per unit strain, is as high as 104, which is 34 times as that in continuous carbon fiber composites without an overlapped part. The results further show that the piezoresistivity curve of overlapped carbon fiber polymer-matrix smart layer is smooth and stable, and exhibits a sensing limit of around 8500 με. An electrical model of the overlapped carbon fiber polymer smart layer was established, which revealed that the change of interlaminar resistance in the overlapping region is the source of its piezoresistivity. Furthermore, a preliminary explanation of the mechanism of the change of interlaminar resistance was made from fiber axial load, overlapped area and interlaminar shear strain.
A smart layer was developed by effectively overlapping continuous carbon fibers in a local area in epoxy matrix. The smart layer was stuck on the st ructure surface to sense its deformation and perform a large-region monitoring. Based on the smart layer, the strain and displacement of the components were detected in the uniaxial tension and three-point bending experiments. The results indicate that the local overlapped structure is the essence of the overlapped carbon fiber polymer-matrix smart layer. The gauge factor of the overlapped carbon fiber polymer-matrix smart layer, defined as fractional change in resistance per unit strain, is as high as 104, which is 34 times as that in continuous carbon fiber composites without an overlapped part. The results further show that the piezoresistivity curve of overlapped carbon fiber polymer-matrix smart layer is smooth and stable, and exhibits a sensing limit of around 8500 με. An electrical model of the overlapped carbon fiber polymer smart layer was established, which revealed that the change of interlaminar resistance in the overlapping region is the source of its piezoresistivity. Furthermore, a preliminary explanation of the mechanism of the change of interlaminar resistance was made from fiber axial load, overlapped area and interlaminar shear strain.
2010, 27(3): 116-121.
Abstract:
A micromechanics based model of bridging fibers was established to study the effects of interface on the tensile modulus and strength of the fiber reinforced ceramic matrix composites. The coefficients of fiber stress uniformity and interface debonding rate were int roduced to characterize the property of the interface with complete debonding and partial debonding, respectively. The result indicates that the higher the coefficients, the lower the modulus while the higher the stress carried by the fibers when the composites fracture. Based on the rule of mixtures, a new strength calculation model was presented. The effects of matrix crack distribution, interface debonding and fiber pullout on the tensile strength were discussed. The results predicted by the model are in good agreement with the experimental data.
A micromechanics based model of bridging fibers was established to study the effects of interface on the tensile modulus and strength of the fiber reinforced ceramic matrix composites. The coefficients of fiber stress uniformity and interface debonding rate were int roduced to characterize the property of the interface with complete debonding and partial debonding, respectively. The result indicates that the higher the coefficients, the lower the modulus while the higher the stress carried by the fibers when the composites fracture. Based on the rule of mixtures, a new strength calculation model was presented. The effects of matrix crack distribution, interface debonding and fiber pullout on the tensile strength were discussed. The results predicted by the model are in good agreement with the experimental data.
2010, 27(3): 122-127.
Abstract:
Transparent nano TiO2-ZrO2/Poly(MMA-co-MSMA) organic-inorganic composite was prepared by an in situ sol-gel process with methyl methacrylate (MMA) and 3-(trimethoxysilyl) propyl methacrylate (MSMA) as couplingagents. Titanium isopropoxide and zirconium n-tetrabutanoxide were used for the synthesis of the titania-zirconia network. The composite was characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet spect rophotometer (UV), Spectro-Ellipsometer, scanning electron microscope (SEM) and thermo-gravimetric analysis (TGA). With the increase of the TiO2-ZrO2 inorganic content, the refractive indices also promote and ultraviolet absorption becomes stronger. At the same time, the nanoparticles size increases from 20～30 nm to 80～ 90 nm and the composite still keeps transparency. Nanocomposite heat resistance shows conspicuous improvement. The highest carbon yield at 800 ℃ improves with the increase of the inorganic content and the best result is 71 %.
Transparent nano TiO2-ZrO2/Poly(MMA-co-MSMA) organic-inorganic composite was prepared by an in situ sol-gel process with methyl methacrylate (MMA) and 3-(trimethoxysilyl) propyl methacrylate (MSMA) as couplingagents. Titanium isopropoxide and zirconium n-tetrabutanoxide were used for the synthesis of the titania-zirconia network. The composite was characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet spect rophotometer (UV), Spectro-Ellipsometer, scanning electron microscope (SEM) and thermo-gravimetric analysis (TGA). With the increase of the TiO2-ZrO2 inorganic content, the refractive indices also promote and ultraviolet absorption becomes stronger. At the same time, the nanoparticles size increases from 20～30 nm to 80～ 90 nm and the composite still keeps transparency. Nanocomposite heat resistance shows conspicuous improvement. The highest carbon yield at 800 ℃ improves with the increase of the inorganic content and the best result is 71 %.
2010, 27(3): 128-133.
Abstract:
Based on the mesoscopic finite element model of particle reinforced composites , the effect s of stochastic properties of SiC particles on the ratcheting behavior of SiCP/6061Al composites were numerically analyzed by employing a 3D multi-particulate unit cell and using an advanced cyclic plastic constitutive model. In the simulation, a 3D multi-particle unit cell containing the stochastic particle properties was first generated by the random sequential adsorption (RSA) method, and then the effects of the number of particles, the particle arrangement, shape, size and their stochastic distributions on the ratcheting of the composites were discussed by the numerical simulations. The results show that the smaller the particulate size and the higher the proportion of the particles distributing near the surface of matrix as well as the more the number of particulates contained in the unit cell, the higher the resistance to the ratcheting deformation. Meanwhile, the modeled composite with uniform distribution of particle size and location presents higher resistance to the ratcheting deformation than that with random dist ribution. The assumptions of spherical particle and its uniform distributions in size and location in the 3D unit cell can provide a reasonable simulation to the ratcheting of the particle reinforced metal matrix composites.
Based on the mesoscopic finite element model of particle reinforced composites , the effect s of stochastic properties of SiC particles on the ratcheting behavior of SiCP/6061Al composites were numerically analyzed by employing a 3D multi-particulate unit cell and using an advanced cyclic plastic constitutive model. In the simulation, a 3D multi-particle unit cell containing the stochastic particle properties was first generated by the random sequential adsorption (RSA) method, and then the effects of the number of particles, the particle arrangement, shape, size and their stochastic distributions on the ratcheting of the composites were discussed by the numerical simulations. The results show that the smaller the particulate size and the higher the proportion of the particles distributing near the surface of matrix as well as the more the number of particulates contained in the unit cell, the higher the resistance to the ratcheting deformation. Meanwhile, the modeled composite with uniform distribution of particle size and location presents higher resistance to the ratcheting deformation than that with random dist ribution. The assumptions of spherical particle and its uniform distributions in size and location in the 3D unit cell can provide a reasonable simulation to the ratcheting of the particle reinforced metal matrix composites.
2010, 27(3): 134-137.
Abstract:
Based on the thermodynamic theory, the adiabatic temperature of NiO/Al aluminothermic system was calculated by computer numeral simulations. The results show that the adiabatic temperature is equal to the boiling point of Ni element (3156 K) when the preheat temperature is below 2790 K. That is to say, to preheat reactants only increases the gasification rate of Ni element. The results also indicate that the just concentration of Al2O3 diluting agent has little effect on the adiabatic temperature of NiO/Al aluminothermic system, which corresponds to phase transformation temperatures of productions.
Based on the thermodynamic theory, the adiabatic temperature of NiO/Al aluminothermic system was calculated by computer numeral simulations. The results show that the adiabatic temperature is equal to the boiling point of Ni element (3156 K) when the preheat temperature is below 2790 K. That is to say, to preheat reactants only increases the gasification rate of Ni element. The results also indicate that the just concentration of Al2O3 diluting agent has little effect on the adiabatic temperature of NiO/Al aluminothermic system, which corresponds to phase transformation temperatures of productions.
2010, 27(3): 138-143.
Abstract:
Diamond/Cu2Ti and DiamondTi/Cu composites with 60 % volume fraction diamond were manufactured by a pressure infilt ration process. The effects of Ti on the microstructure, interface and properties of diamond/copper composites were comparatively analyzed. The results show that the addition of 0. 1 wt% Ti can greatly improve the interface bonding between copper and diamond. Carbide lamellae can be observed obviously on the interface. By contrast, the interface of Diamond/ Cu2Ti composites fabricated by adding Ti element in copper to form Cu2Ti alloy is better than that of DiamondTi/Cu composites (DiamondTi : Diamond coated with Ti). The thermal conductivity of Diamond/Cu2Ti composites is 621 W(m·K)-1 and that of DiamondTi/Cu composites is 403. 5 W(m·K)-1, both of which are higher than the thermal conductivity of Diamond/Cu composites.
Diamond/Cu2Ti and DiamondTi/Cu composites with 60 % volume fraction diamond were manufactured by a pressure infilt ration process. The effects of Ti on the microstructure, interface and properties of diamond/copper composites were comparatively analyzed. The results show that the addition of 0. 1 wt% Ti can greatly improve the interface bonding between copper and diamond. Carbide lamellae can be observed obviously on the interface. By contrast, the interface of Diamond/ Cu2Ti composites fabricated by adding Ti element in copper to form Cu2Ti alloy is better than that of DiamondTi/Cu composites (DiamondTi : Diamond coated with Ti). The thermal conductivity of Diamond/Cu2Ti composites is 621 W(m·K)-1 and that of DiamondTi/Cu composites is 403. 5 W(m·K)-1, both of which are higher than the thermal conductivity of Diamond/Cu composites.
2010, 27(3): 144-149.
Abstract:
By the numerical simulation of the delamination problem of a double-cantilever beam (DCB) , the issues encountered during numerical simulation based on the cohesive zone approach were studied, which was focusd on the quasi-static methods and static methods for calculating the efficiency as well as the stress-strain function of the interface layer for calculating the accuracy and convergence. The calculation implies that the quasi-static method can effectively simulate the process of delamination; and the stress-strain function of the interface layer should have a degenerate course.
By the numerical simulation of the delamination problem of a double-cantilever beam (DCB) , the issues encountered during numerical simulation based on the cohesive zone approach were studied, which was focusd on the quasi-static methods and static methods for calculating the efficiency as well as the stress-strain function of the interface layer for calculating the accuracy and convergence. The calculation implies that the quasi-static method can effectively simulate the process of delamination; and the stress-strain function of the interface layer should have a degenerate course.
2010, 27(3): 150-154.
Abstract:
In aircraftps overall plan design phase, designers have to evaluate the technology maturity of the composite aircraft structure to determine whether the composite will be applied to the given component . A quantitative evaluation method for technology maturity of composite aircraft structure (TEMCAS) is proposed according to technology readiness levels (TRL) standard. This evaluation method divides the technology maturity of the advanced composite aircraft structure into eight scales, covering all research and development processes, i. e. from demand research to production application. This method was further applied to evaluate the technology maturity of advanced technology fuselage composite of Boeing Company. It can be applied in the overall plan design phase to reduce the risk of aircraft-development and the impact of compositeps application on aircraft-development schedule.
In aircraftps overall plan design phase, designers have to evaluate the technology maturity of the composite aircraft structure to determine whether the composite will be applied to the given component . A quantitative evaluation method for technology maturity of composite aircraft structure (TEMCAS) is proposed according to technology readiness levels (TRL) standard. This evaluation method divides the technology maturity of the advanced composite aircraft structure into eight scales, covering all research and development processes, i. e. from demand research to production application. This method was further applied to evaluate the technology maturity of advanced technology fuselage composite of Boeing Company. It can be applied in the overall plan design phase to reduce the risk of aircraft-development and the impact of compositeps application on aircraft-development schedule.
2010, 27(3): 155-161.
Abstract:
The blades of helicopters suffer from centrifugal forces, flap moments, lag moment s and torsion moments. Based on these loading characteristics, the displacement equations of skin and spar were derived through the nonlinear structural model for blades under generalized two dimensional deformation. Based on the Stroh formalism, the asymptotic solutions of stress fields and displacement fields for the delamination crack tip between skin and spar were obtained by applying the interfacial fracture mechanics to anisot ropic bimaterials. Combined with the special solutions, the st resses and stress intensity factors were computed for the delamination crack tip in the adhesive surface between skin and spar of the helicopter blade under centrifugal forces by applying the boundary collocation way, and the results are close to the values by the interface element way. The results show that the way in this paper is effective for analyzing the delamination failure between skin and spar, which could be used as the basis to research the delamination failure of composite blades.
The blades of helicopters suffer from centrifugal forces, flap moments, lag moment s and torsion moments. Based on these loading characteristics, the displacement equations of skin and spar were derived through the nonlinear structural model for blades under generalized two dimensional deformation. Based on the Stroh formalism, the asymptotic solutions of stress fields and displacement fields for the delamination crack tip between skin and spar were obtained by applying the interfacial fracture mechanics to anisot ropic bimaterials. Combined with the special solutions, the st resses and stress intensity factors were computed for the delamination crack tip in the adhesive surface between skin and spar of the helicopter blade under centrifugal forces by applying the boundary collocation way, and the results are close to the values by the interface element way. The results show that the way in this paper is effective for analyzing the delamination failure between skin and spar, which could be used as the basis to research the delamination failure of composite blades.
2010, 27(3): 162-168.
Abstract:
In order to overcome the effect s of FRP multi-interface, high damping characteristics and diversity of the body wave mode on the ultrasonic nondestructive test, a novel technique for detecting delamination is proposed. A PZT transmitter was employed to create the stress waves in the beam, and an optical fiber interferometric sensor was attached to the surface of the beam to detect the stress wave propagation in the beam. By analyzing the propagation characteristics of ultrasound and the wavelet time-frequency spectrum of the signal, the delamination location can be identified. Based on the theoretical analysis and simulation results, the feasibility of delamination detection with the proposed technique is demonst rated.
In order to overcome the effect s of FRP multi-interface, high damping characteristics and diversity of the body wave mode on the ultrasonic nondestructive test, a novel technique for detecting delamination is proposed. A PZT transmitter was employed to create the stress waves in the beam, and an optical fiber interferometric sensor was attached to the surface of the beam to detect the stress wave propagation in the beam. By analyzing the propagation characteristics of ultrasound and the wavelet time-frequency spectrum of the signal, the delamination location can be identified. Based on the theoretical analysis and simulation results, the feasibility of delamination detection with the proposed technique is demonst rated.
2010, 27(3): 169-176.
Abstract:
In order to optimize the carrying capacity of composite stiffened panels, a new design method was proposed using maximum carrying efficiency as an objective. Different compression and bending stiffnessesp matching relationships were discussed for their effects on the critical buckling loads of stiffened panels. The approaching degree of global buckling load, local buckling load and static load was employed as the quantitative standard to scale the structureps carrying efficiency. Under the control of static load, the structural stability was optimized towards the direction of maximum efficiency. An agent model for structure efficiency optimization was built using the panelps macroscopic compression and bending stiffness parameters as variables. This model voids the local optimal point and is more suitable for numerical optimization. The critical buckling load of optimized panel is basically in accordance with the static load applied on it by finite element analysis, which shows a high efficiency and proves the reliability of this method.
In order to optimize the carrying capacity of composite stiffened panels, a new design method was proposed using maximum carrying efficiency as an objective. Different compression and bending stiffnessesp matching relationships were discussed for their effects on the critical buckling loads of stiffened panels. The approaching degree of global buckling load, local buckling load and static load was employed as the quantitative standard to scale the structureps carrying efficiency. Under the control of static load, the structural stability was optimized towards the direction of maximum efficiency. An agent model for structure efficiency optimization was built using the panelps macroscopic compression and bending stiffness parameters as variables. This model voids the local optimal point and is more suitable for numerical optimization. The critical buckling load of optimized panel is basically in accordance with the static load applied on it by finite element analysis, which shows a high efficiency and proves the reliability of this method.
2010, 27(3): 177-183.
Abstract:
The carbonation and permeability properties of ultra high toughness cementitious composites (UHTCC) were investigated through the rapid carbonation test with and without pre-loading, permeability, rapid chloride ions migration test and measurement of free chloride ions. The results show that the carbonation depth of UHTCC is equal to that of the controlled concrete, but the carbonation depth of UHTCC with pre-loading is only 30 %～40 % of the controlled concrete. The impermeability of UHTCC is superior to that of controlled concrete. The permeability coefficient of UHTCC decreases with age increasing, which is 35 % of the controlled concrete when the age was up to 56 days. Rapid chloride ions migration test and measurement of free chloride ions reveal that UHTCC is much better than the concrete in resisting chloride ions penetration.
The carbonation and permeability properties of ultra high toughness cementitious composites (UHTCC) were investigated through the rapid carbonation test with and without pre-loading, permeability, rapid chloride ions migration test and measurement of free chloride ions. The results show that the carbonation depth of UHTCC is equal to that of the controlled concrete, but the carbonation depth of UHTCC with pre-loading is only 30 %～40 % of the controlled concrete. The impermeability of UHTCC is superior to that of controlled concrete. The permeability coefficient of UHTCC decreases with age increasing, which is 35 % of the controlled concrete when the age was up to 56 days. Rapid chloride ions migration test and measurement of free chloride ions reveal that UHTCC is much better than the concrete in resisting chloride ions penetration.
2010, 27(3): 184-189.
Abstract:
In order to study the relationship between concrete damage and the electric resistance change of electric conductive concrete, concrete beams containing nano-meter carbon black or carbon fiber subjected to loading were investigated. The relationship between the resistance change rate of concrete beams and the strain of geometrical neutral axis was established using an analogy method and a experimental data regression. Based on the damaging mechanics theory and the relationship above, the expression between degree of damnification and the rate of resistance change was set up. This self-diagnosis of conductive concrete material provides a new way for the measurement of the internal damage. The results show that the relationship between the rate of resistance change of concrete beams and the strain of the geometrical neutral axis can be well fitted by the exponential decay first order curve before cracking. The sensitivity of the electric conduction concretes can be reflected directly by the slope of the fitted curve, and the degree of concrete damage can be also indirectly responded.
In order to study the relationship between concrete damage and the electric resistance change of electric conductive concrete, concrete beams containing nano-meter carbon black or carbon fiber subjected to loading were investigated. The relationship between the resistance change rate of concrete beams and the strain of geometrical neutral axis was established using an analogy method and a experimental data regression. Based on the damaging mechanics theory and the relationship above, the expression between degree of damnification and the rate of resistance change was set up. This self-diagnosis of conductive concrete material provides a new way for the measurement of the internal damage. The results show that the relationship between the rate of resistance change of concrete beams and the strain of the geometrical neutral axis can be well fitted by the exponential decay first order curve before cracking. The sensitivity of the electric conduction concretes can be reflected directly by the slope of the fitted curve, and the degree of concrete damage can be also indirectly responded.
2010, 27(3): 190-195.
Abstract:
The mixture ratio between host crystal and curing agent of PU resin is calculated by adopting the particle reaction principle based on the same equivalent weight. The results show that the mixture ratio between host crystal and curing agent of PU resin is 100 ∶20～100 ∶26. By the analysis of DSC cures, viscosity2temperature cures, viscosity-time cures and the gelatin time under 25 ℃, the best mixture ratio of 100 ∶20 is confirmed. In order to test and verify its operational performance, the adhesive strength between the resin and the pipeline wall was simulated nd tested. The results show that the adhesive strength of the resin with mixture ratio of 100 ∶20 is so high that it can meet the requirements of the pipeline lining rehabilitation technology.
The mixture ratio between host crystal and curing agent of PU resin is calculated by adopting the particle reaction principle based on the same equivalent weight. The results show that the mixture ratio between host crystal and curing agent of PU resin is 100 ∶20～100 ∶26. By the analysis of DSC cures, viscosity2temperature cures, viscosity-time cures and the gelatin time under 25 ℃, the best mixture ratio of 100 ∶20 is confirmed. In order to test and verify its operational performance, the adhesive strength between the resin and the pipeline wall was simulated nd tested. The results show that the adhesive strength of the resin with mixture ratio of 100 ∶20 is so high that it can meet the requirements of the pipeline lining rehabilitation technology.
2010, 27(3): 196-199.
Abstract:
In order to avoid the creases and ret ractation of the tubular textile composite in the pipeline because of design irrationality of pipediameter of tubular textile composite, the principle of the design was int roduced, and the elasticity and hot shrinkage property of the tubular textile composite as the key factors were proposed. The strain in the circular direction was analyzed by the finite element when the tubular textile composite was inversed. The results show that the design data of the pipediameter should be adjusted depending on the elasticity of the tubular textile composite. The hot shrinkage property was analysed by the software of SPSS and a model related with hot shrinkage, temperature and time was established.
In order to avoid the creases and ret ractation of the tubular textile composite in the pipeline because of design irrationality of pipediameter of tubular textile composite, the principle of the design was int roduced, and the elasticity and hot shrinkage property of the tubular textile composite as the key factors were proposed. The strain in the circular direction was analyzed by the finite element when the tubular textile composite was inversed. The results show that the design data of the pipediameter should be adjusted depending on the elasticity of the tubular textile composite. The hot shrinkage property was analysed by the software of SPSS and a model related with hot shrinkage, temperature and time was established.
