2007 Vol. 24, No. 6
2007, 24(6): 1-6.
Abstract:
The bagasse fiber reinforced polypropylene composites were fabricated by injection molding, and the mechanical properties of the composites were investigated in terms of the effects of fiber mass fraction, injection molding conditions and additive. The results indicate that the flexural modulus increases with the increase of fiber mass fraction. All the mechanical properties decrease with the increase of cylinder temperature due to the thermal degradation of the bagasse fibers. Under the conditions of mold temperature 90 ℃, 30 s interval, and different cylinder temperatures 185 ℃ and 165 ℃, the flexural properties and the impact strength show the maximum values, respectively. After the addition of maleic anhydride grafted polypropylene, the flexural strength and the impact strength are improved.
The bagasse fiber reinforced polypropylene composites were fabricated by injection molding, and the mechanical properties of the composites were investigated in terms of the effects of fiber mass fraction, injection molding conditions and additive. The results indicate that the flexural modulus increases with the increase of fiber mass fraction. All the mechanical properties decrease with the increase of cylinder temperature due to the thermal degradation of the bagasse fibers. Under the conditions of mold temperature 90 ℃, 30 s interval, and different cylinder temperatures 185 ℃ and 165 ℃, the flexural properties and the impact strength show the maximum values, respectively. After the addition of maleic anhydride grafted polypropylene, the flexural strength and the impact strength are improved.
2007, 24(6): 7-12.
Abstract:
Through the method of grafting coupling agents with different chain lengths onto the surface of carbon fiber, the influence of chain lengths on interfacial performances of carbon fiber/polyarylacetylene composites was studied. Surface energy of carbon fiber before and after treatment was measured and the relation between surface energy and fiber wettability was discussed. At the same time, the interfacial adhesion was evaluated by interlaminar shear strength, and the failure mechanisms of composites were analyzed by fracture morphologies. The results indicate that with the increase in chain lengths of coupling agents on the carbon fiber surface, the interfacial adhesion of composites increases greatly. The main mechanism responsible for the improvement of interfacial adhesion is the entanglement interaction between the molecular chain of coupling agent on carbon fiber and the counterpart of polyarylacetylene resin at the interface. Moreover, the longer the chain length on the carbon fiber surface, the stronger the entanglement at the composite interface.
Through the method of grafting coupling agents with different chain lengths onto the surface of carbon fiber, the influence of chain lengths on interfacial performances of carbon fiber/polyarylacetylene composites was studied. Surface energy of carbon fiber before and after treatment was measured and the relation between surface energy and fiber wettability was discussed. At the same time, the interfacial adhesion was evaluated by interlaminar shear strength, and the failure mechanisms of composites were analyzed by fracture morphologies. The results indicate that with the increase in chain lengths of coupling agents on the carbon fiber surface, the interfacial adhesion of composites increases greatly. The main mechanism responsible for the improvement of interfacial adhesion is the entanglement interaction between the molecular chain of coupling agent on carbon fiber and the counterpart of polyarylacetylene resin at the interface. Moreover, the longer the chain length on the carbon fiber surface, the stronger the entanglement at the composite interface.
2007, 24(6): 13-18.
Abstract:
To achieve a better interfacial adhesion between the fiber and matrix in composites, the continuous carbon fiber bundle was separated to the single fiber tape by the self-made air comb, then modified by the polyphenol film, which was electropolymerized by a cyclic voltammogram technique. The IR spectrum indicates that the polyphenol film formed on the carbon fiber surface with amounts of active agents such as hydroxyl and ether group can enhance the interfacial adhesion between the carbon fiber and the epoxy resin of the composites. Compared with the epoxy resin composites reinforced by the carbon fiber without surface modification, the strength of transverse tension, longitudinal tension, and interlaminar shear of the epoxy resin composites reinforced by the carbon fiber tape modified with polyphenol film are improved by 90%, 45% and 110%, respectively. The experimental results also show that the carbon tape can increase the mechanical properties of the composites, much better than the carbon fiber bundle.
To achieve a better interfacial adhesion between the fiber and matrix in composites, the continuous carbon fiber bundle was separated to the single fiber tape by the self-made air comb, then modified by the polyphenol film, which was electropolymerized by a cyclic voltammogram technique. The IR spectrum indicates that the polyphenol film formed on the carbon fiber surface with amounts of active agents such as hydroxyl and ether group can enhance the interfacial adhesion between the carbon fiber and the epoxy resin of the composites. Compared with the epoxy resin composites reinforced by the carbon fiber without surface modification, the strength of transverse tension, longitudinal tension, and interlaminar shear of the epoxy resin composites reinforced by the carbon fiber tape modified with polyphenol film are improved by 90%, 45% and 110%, respectively. The experimental results also show that the carbon tape can increase the mechanical properties of the composites, much better than the carbon fiber bundle.
2007, 24(6): 19-25.
Abstract:
In order to investigate the mechanical properties of commercial plastic polypropylene (PP) reinforced with inorganic rigid particles, the PP composite material filled with the surface-modified silica particles by silane coupling agent A-151 was prepared by the melt blending method. The effects of the particle size, mass fraction of silica, surface modification of silica and mixture of the silica particles with different sizes on the toughening and strengthening of PP matrix were investigated based on the results of mechanical properties testing and the observation of the impact fracture surface morphology of the composites. The results show that the toughness, strength and rigidity of the composites can be improved simultaneously by filling nano silica particles into polypropylene. The finer the size of the particles is, the higher the mechanical properties of the composites are. When the modified silica particles are filled into PP, the dispersion of the silica in PP matrix and the compatibility between the silica and matrix are improved, and the mechanical properties of the composites are improved. The composites reinforced with the mixture of the silica particles with different sizes have higher tensile and flexural properties. The mixture has a better reinforcing effect on PP matrix, but the impact property of the composites decreases.
In order to investigate the mechanical properties of commercial plastic polypropylene (PP) reinforced with inorganic rigid particles, the PP composite material filled with the surface-modified silica particles by silane coupling agent A-151 was prepared by the melt blending method. The effects of the particle size, mass fraction of silica, surface modification of silica and mixture of the silica particles with different sizes on the toughening and strengthening of PP matrix were investigated based on the results of mechanical properties testing and the observation of the impact fracture surface morphology of the composites. The results show that the toughness, strength and rigidity of the composites can be improved simultaneously by filling nano silica particles into polypropylene. The finer the size of the particles is, the higher the mechanical properties of the composites are. When the modified silica particles are filled into PP, the dispersion of the silica in PP matrix and the compatibility between the silica and matrix are improved, and the mechanical properties of the composites are improved. The composites reinforced with the mixture of the silica particles with different sizes have higher tensile and flexural properties. The mixture has a better reinforcing effect on PP matrix, but the impact property of the composites decreases.
2007, 24(6): 26-30.
Abstract:
A sol-gel in-situ method was used to synthesize the nano-ZnS/PVDF composite film by using ZnAC2 ·2H2O and PVDF as the primary materials, and DMF as the solvent. The results analyzed by XRD and TEM exhibit that the ZnS nanoparticles are well distributed in PVDF films and their size can be controlled in the range of 3nm to 7nm. The studies on the UV-VIS absorption spectroscopy show an observable blue-shift with the decrease of the crystal size of ZnS. The fluorescence spectroscopies indicate both the photoemission of recombination with the exciton peaking at 368nm and the emission at 429nm termed 'self-activated’. The optical properties of this composite film are not essentially impacted by adding of dispersant, but the growth of ZnS is limited and the dispersity of these nanoparticles is improved.
A sol-gel in-situ method was used to synthesize the nano-ZnS/PVDF composite film by using ZnAC2 ·2H2O and PVDF as the primary materials, and DMF as the solvent. The results analyzed by XRD and TEM exhibit that the ZnS nanoparticles are well distributed in PVDF films and their size can be controlled in the range of 3nm to 7nm. The studies on the UV-VIS absorption spectroscopy show an observable blue-shift with the decrease of the crystal size of ZnS. The fluorescence spectroscopies indicate both the photoemission of recombination with the exciton peaking at 368nm and the emission at 429nm termed 'self-activated’. The optical properties of this composite film are not essentially impacted by adding of dispersant, but the growth of ZnS is limited and the dispersity of these nanoparticles is improved.
2007, 24(6): 31-35.
Abstract:
A new kind of material for oil adsorption was prepared by melt blending with EPDM as the matrix and Fe2O3 as the filler. The effects of dicumylperoxide(DCP)and Fe2O3 contents on the oil absorptivity were studied. The results show that the oil absorptivity reaches the highest value for the Fe2O3/EPDM composite with 3 wt% DCP and 25 wt% Fe2O3, while the same is true for Fe2O3(calcination)/EPDM composite with 2 wt% DCP and 30 wt% Fe2O3. Comparing the two samples with the highest oil absorptivity, the oil absorption rate of Fe2O3(calcination)/EPDM composite is higher. The experimental result indicates that the oil absorptivity of Fe2O3/EPDM composite is 227% higher than that of EPDM (crosslinked); the oil absorptivity of Fe2O3(calcination)/EPDM composite is 64% higher than that of Fe2O3/EPDM composite. It is considered that Fe2O3 could reduce some intermolecular interaction of polymer chains to form many channels in the network structure and increase the cubage in network structure. So the oil molecule can come into the network structure easily. The absorbent characteristics of Fe2O3(calcination)/EPDM are better than those of Fe2O3/EPDM.
A new kind of material for oil adsorption was prepared by melt blending with EPDM as the matrix and Fe2O3 as the filler. The effects of dicumylperoxide(DCP)and Fe2O3 contents on the oil absorptivity were studied. The results show that the oil absorptivity reaches the highest value for the Fe2O3/EPDM composite with 3 wt% DCP and 25 wt% Fe2O3, while the same is true for Fe2O3(calcination)/EPDM composite with 2 wt% DCP and 30 wt% Fe2O3. Comparing the two samples with the highest oil absorptivity, the oil absorption rate of Fe2O3(calcination)/EPDM composite is higher. The experimental result indicates that the oil absorptivity of Fe2O3/EPDM composite is 227% higher than that of EPDM (crosslinked); the oil absorptivity of Fe2O3(calcination)/EPDM composite is 64% higher than that of Fe2O3/EPDM composite. It is considered that Fe2O3 could reduce some intermolecular interaction of polymer chains to form many channels in the network structure and increase the cubage in network structure. So the oil molecule can come into the network structure easily. The absorbent characteristics of Fe2O3(calcination)/EPDM are better than those of Fe2O3/EPDM.
2007, 24(6): 36-43.
Abstract:
EPDM/PS alternative multilayer composites were prepared by micro-or nano-layer coextrusion system designed in this lab. The results of polar light microscope (PLM) and scanning electrical microscope (SEM) analysis indicate that the composites have the alternative multilayer structure. Compared to conventional blends, the fracture behavior of EPDM/PS alternative 64-layer composites is much different, which includes two stages: the PS layers break first, followed by only the EPDM layers elongated. Because both PS and EPDM layers are continuous and EPDM layers prevent the cracks or crazes developing between the nearby PS layers, the tensile strength and the Youngs modulus of the 64-layer composites are higher than those of the corresponding conventional blends. The effects of SEBS as a compatibilizer added into PS phase on the mechanical properties of EPDM/PS alternative multilayer composites were investigated. The results indicate that the interfacial adhesion strength between EPDM layers and PS layers and the toughness of the PS layers are improved in the presence of SEBS.
EPDM/PS alternative multilayer composites were prepared by micro-or nano-layer coextrusion system designed in this lab. The results of polar light microscope (PLM) and scanning electrical microscope (SEM) analysis indicate that the composites have the alternative multilayer structure. Compared to conventional blends, the fracture behavior of EPDM/PS alternative 64-layer composites is much different, which includes two stages: the PS layers break first, followed by only the EPDM layers elongated. Because both PS and EPDM layers are continuous and EPDM layers prevent the cracks or crazes developing between the nearby PS layers, the tensile strength and the Youngs modulus of the 64-layer composites are higher than those of the corresponding conventional blends. The effects of SEBS as a compatibilizer added into PS phase on the mechanical properties of EPDM/PS alternative multilayer composites were investigated. The results indicate that the interfacial adhesion strength between EPDM layers and PS layers and the toughness of the PS layers are improved in the presence of SEBS.
2007, 24(6): 44-49.
Abstract:
The hindered phenol AO-80/nitrile-butadiene rubber (NBR)/poly(vinyl chloride) (PVC) crosslinking composites were prepared and their microstructure and dynamic mechanical properties were investigated. SEM and TEM prove that the majority of AO-80 dissolve in the NBR/PVC matrix and the remnants AO-80 in the submicro-size particles distribute in the matrix. The DSC and XRD results illustrate that AO-80 in the matrix exists in an amorphous form. The results of DSC and DMTA prove that strong intermolecular interactions are formed between AO-80 and NBR/PVC matrix. All the AO-80/NBR/PVC crosslinking composites have only one tanδ peak, which displays the excellent compatibility between the AO-80 and the NBR/PVC matrix. More importantly, the tanδ peaks of the crosslinking composites shift to the higher temperature with increasing of the AO-80 amount in the composites, and the tanδ value of the crosslinking composites obviously synchronously increases. The chemical crosslinking of the composites results in considerable tensile strength. The high damping and mechanical properties endow the composites with a potential and promising application future in engineering.
The hindered phenol AO-80/nitrile-butadiene rubber (NBR)/poly(vinyl chloride) (PVC) crosslinking composites were prepared and their microstructure and dynamic mechanical properties were investigated. SEM and TEM prove that the majority of AO-80 dissolve in the NBR/PVC matrix and the remnants AO-80 in the submicro-size particles distribute in the matrix. The DSC and XRD results illustrate that AO-80 in the matrix exists in an amorphous form. The results of DSC and DMTA prove that strong intermolecular interactions are formed between AO-80 and NBR/PVC matrix. All the AO-80/NBR/PVC crosslinking composites have only one tanδ peak, which displays the excellent compatibility between the AO-80 and the NBR/PVC matrix. More importantly, the tanδ peaks of the crosslinking composites shift to the higher temperature with increasing of the AO-80 amount in the composites, and the tanδ value of the crosslinking composites obviously synchronously increases. The chemical crosslinking of the composites results in considerable tensile strength. The high damping and mechanical properties endow the composites with a potential and promising application future in engineering.
2007, 24(6): 50-56.
Abstract:
The saturated permeability tensor of composite preforms was predicted by the combination of homogenization theory and computational fluid dynamics technique. Generalized Darcys law was first derived from the study of fluid flow through a solid-fluid mixture, and the saturated permeability tensor of a preform could be predicted by studying its unit cell under periodic boundary conditions. The efficiency of this method was validated by conventional analytical methods for unidirectional fabrics. For preforms with complex microstructure, the permeability prediction involved two steps. First, the effective permeability values of the open channel and tows of the unit cell were determined respectively, and the overall permeability was determined accordingly. For a plane-weave fabric, the results obtained here are in good agreement with other methods and experimental results. The effects of unit cell microstructure were also investigated. The analyses show that the permeability values may differ from each other significantly for preforms with equal porosities, similar microstructures but different inter-tow channel configurations.
The saturated permeability tensor of composite preforms was predicted by the combination of homogenization theory and computational fluid dynamics technique. Generalized Darcys law was first derived from the study of fluid flow through a solid-fluid mixture, and the saturated permeability tensor of a preform could be predicted by studying its unit cell under periodic boundary conditions. The efficiency of this method was validated by conventional analytical methods for unidirectional fabrics. For preforms with complex microstructure, the permeability prediction involved two steps. First, the effective permeability values of the open channel and tows of the unit cell were determined respectively, and the overall permeability was determined accordingly. For a plane-weave fabric, the results obtained here are in good agreement with other methods and experimental results. The effects of unit cell microstructure were also investigated. The analyses show that the permeability values may differ from each other significantly for preforms with equal porosities, similar microstructures but different inter-tow channel configurations.
2007, 24(6): 57-62.
Abstract:
In order to investigate the unsaturated impregnation property of resin along the thickness of fiber stacks at high temperature during the process of resin film infusion(RFI), the influence factors of the flow front of resin were studied, and the effects of the primary factors on the impregnation velocity of liquids along the thickness of glass fiber weaves and the rules were tested and analyzed by using the self-designed equipment. The results indicate that the resin infusion along the thickness of fiber stacks is one-dimensional flow, and the impregnation velocity of liquids can be increased by increasing the vacuum pressure, raising the temperature of resin and reducing the volume fraction of fibers. In addition, the impregnation behaviors of E-51 epoxy resin at 70 ℃ and silicone oil at room temperature along the thickness of glass fiber plies are almost homological.
In order to investigate the unsaturated impregnation property of resin along the thickness of fiber stacks at high temperature during the process of resin film infusion(RFI), the influence factors of the flow front of resin were studied, and the effects of the primary factors on the impregnation velocity of liquids along the thickness of glass fiber weaves and the rules were tested and analyzed by using the self-designed equipment. The results indicate that the resin infusion along the thickness of fiber stacks is one-dimensional flow, and the impregnation velocity of liquids can be increased by increasing the vacuum pressure, raising the temperature of resin and reducing the volume fraction of fibers. In addition, the impregnation behaviors of E-51 epoxy resin at 70 ℃ and silicone oil at room temperature along the thickness of glass fiber plies are almost homological.
2007, 24(6): 63-67.
Abstract:
The non-isothermal differential scanning calorimetry (DSC) technique was used to study the cure kinetics of the resin system for the CFRP pressure vessel. The activation energy of the resin system was estimated by the isoconversional method. The reaction mechanism was assumed to subject to an autocatalytic equation. The interval method presented in this paper was used to establish a cure kinetics model for the resin system. According to the temperature test during the curing process, the result calculated using the cure kinetics model shows a good match with the experimental data, which indicates that the cure kinetic model established by the interval method can present a necessary sub-model for simulating the temperature and residual stress fields of the CFRP pressure vessel with an ultrathin metallic liner.
The non-isothermal differential scanning calorimetry (DSC) technique was used to study the cure kinetics of the resin system for the CFRP pressure vessel. The activation energy of the resin system was estimated by the isoconversional method. The reaction mechanism was assumed to subject to an autocatalytic equation. The interval method presented in this paper was used to establish a cure kinetics model for the resin system. According to the temperature test during the curing process, the result calculated using the cure kinetics model shows a good match with the experimental data, which indicates that the cure kinetic model established by the interval method can present a necessary sub-model for simulating the temperature and residual stress fields of the CFRP pressure vessel with an ultrathin metallic liner.
2007, 24(6): 68-76.
Abstract:
Polycarbosilane (PCS) fibers cured in 1-hexyne vapor have much less oxygen than those cured by air. The composition and structure of PCS fibers transform during 1-hexyne curing process. The results show that the reaction degree of Si—H bond and gel content of PCS fibers rapidly increase when the curing temperature increases. Si—H and Si—CH3 bonds in PCS are induced by 1-hexyne to cleavage and form Si-central radicals. Fully developed crosslinking fibers come into being through the combination of these radicals. And a small amount of hexyl is introduced to PCS structure during the reaction. The tensile strength of SiC fibers prepared is 2.79GPa and the oxygen content is 5wt%~6wt%. The fibers show better high temperature resistance than Nicalon fibers. After being exposed in Ar to 1300℃, the SiC fibers maintain 80% of the initial strength; after being exposed in Ar to 1400℃, they maintain 60% of the initial strength. And during the heat treatment from 1300℃ to 1600℃, the change of β-SiCs grain size is only 2.18nm.
Polycarbosilane (PCS) fibers cured in 1-hexyne vapor have much less oxygen than those cured by air. The composition and structure of PCS fibers transform during 1-hexyne curing process. The results show that the reaction degree of Si—H bond and gel content of PCS fibers rapidly increase when the curing temperature increases. Si—H and Si—CH3 bonds in PCS are induced by 1-hexyne to cleavage and form Si-central radicals. Fully developed crosslinking fibers come into being through the combination of these radicals. And a small amount of hexyl is introduced to PCS structure during the reaction. The tensile strength of SiC fibers prepared is 2.79GPa and the oxygen content is 5wt%~6wt%. The fibers show better high temperature resistance than Nicalon fibers. After being exposed in Ar to 1300℃, the SiC fibers maintain 80% of the initial strength; after being exposed in Ar to 1400℃, they maintain 60% of the initial strength. And during the heat treatment from 1300℃ to 1600℃, the change of β-SiCs grain size is only 2.18nm.
2007, 24(6): 77-82.
Abstract:
In order to study the corrosion property of a kind of domestic continuous basalt fiber BF-CSH-01, the mass loss, monofilament strength, tensile properties of tows and flexural strength of the composites were investigated in different immersion periods of sodium hydroxide and hydrochloric acid of 2mol/L at 80℃. The results indicate that the acid resistance of this basalt fiber is better than the alkali resistance, which is contrary to BF-CMD-01 basalt fiber studied before. The tensile strength of BF-CSH-01 monofilament declines synchronously with the mass in acid mediums, while the tensile strength declines intensively with the little mass change in alkali mediums. The acid and alkali have a great effect on the tensile strength of the tows and on the flexural strength of its reinforced composites. The regularity of strength is in conformity to monofilament while the modulus is insensitive.
In order to study the corrosion property of a kind of domestic continuous basalt fiber BF-CSH-01, the mass loss, monofilament strength, tensile properties of tows and flexural strength of the composites were investigated in different immersion periods of sodium hydroxide and hydrochloric acid of 2mol/L at 80℃. The results indicate that the acid resistance of this basalt fiber is better than the alkali resistance, which is contrary to BF-CMD-01 basalt fiber studied before. The tensile strength of BF-CSH-01 monofilament declines synchronously with the mass in acid mediums, while the tensile strength declines intensively with the little mass change in alkali mediums. The acid and alkali have a great effect on the tensile strength of the tows and on the flexural strength of its reinforced composites. The regularity of strength is in conformity to monofilament while the modulus is insensitive.
2007, 24(6): 83-88.
Abstract:
The artificial neutral network (ANN) method is applied to the prediction on the ablative performance of carbon/carbon composites. The key control factors for the ablative performance, namely, the density, degree of graphitization and the matrix kind, were selected. Further, a relation between those factors and ablative performance was determined. Through large numbers of experimental data, the structure and the performance of ANN had been evaluated with the variation of training parameters. It can be achieved from the results that there exists an optimal predicting ratio when the training set scale, the hidden unit, initial learning rate and momentum coefficient are 35, 7, 0.5 and 0.2, respectively. Based on the ratio, prediction and evaluation on the mass ablative rate have been made for the ablative performance of carbon/carbon composites. With the application of ANN, the prediction error is within 11%, which can satisfy the precision requirements for practical engineering purposes.
The artificial neutral network (ANN) method is applied to the prediction on the ablative performance of carbon/carbon composites. The key control factors for the ablative performance, namely, the density, degree of graphitization and the matrix kind, were selected. Further, a relation between those factors and ablative performance was determined. Through large numbers of experimental data, the structure and the performance of ANN had been evaluated with the variation of training parameters. It can be achieved from the results that there exists an optimal predicting ratio when the training set scale, the hidden unit, initial learning rate and momentum coefficient are 35, 7, 0.5 and 0.2, respectively. Based on the ratio, prediction and evaluation on the mass ablative rate have been made for the ablative performance of carbon/carbon composites. With the application of ANN, the prediction error is within 11%, which can satisfy the precision requirements for practical engineering purposes.
2007, 24(6): 89-94.
Abstract:
The bioactive apatite coatings were prepared on the surface of carbon/carbon composites using the method of sono-electrodeposition. The effects of NaF treatment on the morphology, structure and composition of the as-received coatings were investigated by SEM, EDAX, FTIR and XRD. The results show that NaF promotes the change of tricalcium phosphate to fluoridated hydroxyapatite together with increasing the crystallization degree of the coating. After being treated with NaF, the composition of the coating is a mixture of hydroxyapatite(HA) and F-rich apatite (FHA). The coatings are both plate-like crystals before and after treatment, however, the size of the crystals increases after treatment. The bonding strength between the coating and C/C matrix increases slightly after being treated with NaF, the bonding strength can reach 4.08MPa, and the fluorine content of the coating was 4.59wt%. In addition, the reaction mechanism of hydroxyapatite transformed to fluorine-containing hydroxyapatite was also discussed. To obtain fluorine-containing hydroxyapatite coatings with the treatment by NaF, it is necessary to introduce phosphate in the immersion solution in order to maintain the pH.
The bioactive apatite coatings were prepared on the surface of carbon/carbon composites using the method of sono-electrodeposition. The effects of NaF treatment on the morphology, structure and composition of the as-received coatings were investigated by SEM, EDAX, FTIR and XRD. The results show that NaF promotes the change of tricalcium phosphate to fluoridated hydroxyapatite together with increasing the crystallization degree of the coating. After being treated with NaF, the composition of the coating is a mixture of hydroxyapatite(HA) and F-rich apatite (FHA). The coatings are both plate-like crystals before and after treatment, however, the size of the crystals increases after treatment. The bonding strength between the coating and C/C matrix increases slightly after being treated with NaF, the bonding strength can reach 4.08MPa, and the fluorine content of the coating was 4.59wt%. In addition, the reaction mechanism of hydroxyapatite transformed to fluorine-containing hydroxyapatite was also discussed. To obtain fluorine-containing hydroxyapatite coatings with the treatment by NaF, it is necessary to introduce phosphate in the immersion solution in order to maintain the pH.
2007, 24(6): 95-99.
Abstract:
Shear lag analysis was applied to bone-like nanostructural biomaterials such as nacre and bone with unique structure in nano scale. The models for protein with both linear and elastic-plastic deformations were developed. Compared with the results of finite element method (FEM) and the tension shear chain model of Gao, the linear shear lag model fits better with FEM while the tension shear chain model predicts a larger effective modulus when the aspect ratio is large. The elastic-plastic shear lag model fits well with the experimental results, and the plastic deformation takes place before the modulus of the materials decreases obviously, which provides those materials the ability to dissipate energy and enhance the toughness.
Shear lag analysis was applied to bone-like nanostructural biomaterials such as nacre and bone with unique structure in nano scale. The models for protein with both linear and elastic-plastic deformations were developed. Compared with the results of finite element method (FEM) and the tension shear chain model of Gao, the linear shear lag model fits better with FEM while the tension shear chain model predicts a larger effective modulus when the aspect ratio is large. The elastic-plastic shear lag model fits well with the experimental results, and the plastic deformation takes place before the modulus of the materials decreases obviously, which provides those materials the ability to dissipate energy and enhance the toughness.
2007, 24(6): 100-104.
Abstract:
The strength, molecular weight and morphology of β-calcium metaphosphate whiskers/poly L-lactide composites (β-CMPW/PLLA) for internal fixation of bone fractures were measured after degradation in the simulated body fluid. The results indicate that the compress strength of the composites can maintain in 8 weeks. The strength of 25wt% β-CMPW/75wt% PLLA maintains at 103 MPa in 20 weeks, and the strength of 45wt% β-CMPW/55wt% PLLA drops to approximately 88% of the initial value in 12 weeks. The scanning electron microscope (SEM) images show that PLLA disappears increasingly and a few pores are formed on the rods surface of the samples. The pH value of the simulated body fluid can keep stabilization during degradation. Gel permeation chromatography(GPC) patterns show that the molecular weight of PLLA significantly decreases with the immersion time. The number-average molecular weight is about 200000 and the weight-average drops 32% after degradation for 20 weeks.
The strength, molecular weight and morphology of β-calcium metaphosphate whiskers/poly L-lactide composites (β-CMPW/PLLA) for internal fixation of bone fractures were measured after degradation in the simulated body fluid. The results indicate that the compress strength of the composites can maintain in 8 weeks. The strength of 25wt% β-CMPW/75wt% PLLA maintains at 103 MPa in 20 weeks, and the strength of 45wt% β-CMPW/55wt% PLLA drops to approximately 88% of the initial value in 12 weeks. The scanning electron microscope (SEM) images show that PLLA disappears increasingly and a few pores are formed on the rods surface of the samples. The pH value of the simulated body fluid can keep stabilization during degradation. Gel permeation chromatography(GPC) patterns show that the molecular weight of PLLA significantly decreases with the immersion time. The number-average molecular weight is about 200000 and the weight-average drops 32% after degradation for 20 weeks.
2007, 24(6): 105-109.
Abstract:
A series of macroporous calcium polyphosphate/chitosan(CPP/CS) composite rod and microporous CPP/CS composite particle were synthesized with CPP and CS using two technologies by a heat-dispersion suspension complex method. The structure and morphology of the composites were measured by IR spectrum and SEM. The hydrogen bond was formed between —NH2 of CS and —P O of CPP in the composites. The aperture of the macroporous composite is about 50~300μm, the porocity is 71.13%, which was determined by the ethanol infiltration method. And for the microporous composites, the aperture and porocity are 10~100μm and 40.76%, respectively. The former is suitable for the need of bone tissue engineering scaffold material, but the later is not suitable. The cell compatibility of macroporous composite was better than that of microporous composite. The cell compatibility is the best when CPP/CS=7/3. The compression strength of CPP is increased by the complex method. And the compression strength of composite is also the highest when CPP/CS=7/3.
A series of macroporous calcium polyphosphate/chitosan(CPP/CS) composite rod and microporous CPP/CS composite particle were synthesized with CPP and CS using two technologies by a heat-dispersion suspension complex method. The structure and morphology of the composites were measured by IR spectrum and SEM. The hydrogen bond was formed between —NH2 of CS and —P O of CPP in the composites. The aperture of the macroporous composite is about 50~300μm, the porocity is 71.13%, which was determined by the ethanol infiltration method. And for the microporous composites, the aperture and porocity are 10~100μm and 40.76%, respectively. The former is suitable for the need of bone tissue engineering scaffold material, but the later is not suitable. The cell compatibility of macroporous composite was better than that of microporous composite. The cell compatibility is the best when CPP/CS=7/3. The compression strength of CPP is increased by the complex method. And the compression strength of composite is also the highest when CPP/CS=7/3.
2007, 24(6): 110-115.
Abstract:
17Ni/(10NiO-NiFe2O4) cermets added with CaO were fabricated by cold pressing-sintering. The effects of CaO content and sintering temperature on the phase composition, relative density and mechanical properties of 17Ni/(10NiO-NiFe2O4) cermets were studied. The results show that the cermets consist of Ni, NiO and NiFe2O4. Introduction of CaO can accelerate the densification of 10NiO-NiFe2O4 composites. As the sintering temperature is limited at 1250℃, the relative density will achieve the maximum value of 98.75% for the sample doped 1.0wt% CaO, and then decrease with increasing the CaO content sequentially. With the temperature increasing from 1250℃ to 1350℃, the relative densities reveal the increase for the samples containing CaO with the content less than 0.5wt% and the decrease for the samples containing more than 0.5wt% CaO. Both increasing sintering temperature and adding CaO cause grow-up of the ceramic grain. An optimal bending strength value of 150.66MPa of the sample sintered at 1250℃, is achieved at the CaO content of 1.0%.
17Ni/(10NiO-NiFe2O4) cermets added with CaO were fabricated by cold pressing-sintering. The effects of CaO content and sintering temperature on the phase composition, relative density and mechanical properties of 17Ni/(10NiO-NiFe2O4) cermets were studied. The results show that the cermets consist of Ni, NiO and NiFe2O4. Introduction of CaO can accelerate the densification of 10NiO-NiFe2O4 composites. As the sintering temperature is limited at 1250℃, the relative density will achieve the maximum value of 98.75% for the sample doped 1.0wt% CaO, and then decrease with increasing the CaO content sequentially. With the temperature increasing from 1250℃ to 1350℃, the relative densities reveal the increase for the samples containing CaO with the content less than 0.5wt% and the decrease for the samples containing more than 0.5wt% CaO. Both increasing sintering temperature and adding CaO cause grow-up of the ceramic grain. An optimal bending strength value of 150.66MPa of the sample sintered at 1250℃, is achieved at the CaO content of 1.0%.
2007, 24(6): 116-120.
Abstract:
The Ni-W-ZrO2 composite coatings were prepared by electrodeposition. The dispersible characteristics of particles were studied. The effects of the main factors, such as adding particle quantity, current density, pH value and temperature on the hardness, deposition rate and surface of Ni-W-ZrO2 composite coatings were investigated. The process parameters of Ni-W-ZrO2 composite coatings were obtained through optimization: the adding particle quantity is 10 g/L, current density is 15 A/dm2, pH value is 7 and temperature is 60~70 ℃. The microhardness of Ni-W-ZrO2 coatings reaches higher than HV800(×9.8MPa). The corrosion resistance was studied by the electrochemical techniques, and the results show that the Ni-W-ZrO2 composite coatings have obvious passivation.
The Ni-W-ZrO2 composite coatings were prepared by electrodeposition. The dispersible characteristics of particles were studied. The effects of the main factors, such as adding particle quantity, current density, pH value and temperature on the hardness, deposition rate and surface of Ni-W-ZrO2 composite coatings were investigated. The process parameters of Ni-W-ZrO2 composite coatings were obtained through optimization: the adding particle quantity is 10 g/L, current density is 15 A/dm2, pH value is 7 and temperature is 60~70 ℃. The microhardness of Ni-W-ZrO2 coatings reaches higher than HV800(×9.8MPa). The corrosion resistance was studied by the electrochemical techniques, and the results show that the Ni-W-ZrO2 composite coatings have obvious passivation.
2007, 24(6): 121-127.
Abstract:
Based on the Tsai-Hill failure criterion and the cohesive zone model, a computational model was proposed to predict a typical damaged mode for honeycomb sandwich panels containing interfacial debonding under end compressive loading. The proposed model was built up based on a new failure mode, which is observed in the double cantilever beam (DCB) and the single leg bending (SLB) tests for honeycomb sandwich panels. The prediction results show that the end compressive failure occurs according to the following procedure: starting with local buckling of the debonding facesheet, followed by the initiation of interlaminar delamination between 45° ply and 0° ply, and meanwhile, the fracture of 45° ply, then the rapid propagation of interlaminar delamination between 45° ply and 0° ply, and finally, ending in the symmetrical global buckling of facesheets. Compared with the results of the end compressive test, the new failure mode predicted in the simulation is validated well in the experiment.
Based on the Tsai-Hill failure criterion and the cohesive zone model, a computational model was proposed to predict a typical damaged mode for honeycomb sandwich panels containing interfacial debonding under end compressive loading. The proposed model was built up based on a new failure mode, which is observed in the double cantilever beam (DCB) and the single leg bending (SLB) tests for honeycomb sandwich panels. The prediction results show that the end compressive failure occurs according to the following procedure: starting with local buckling of the debonding facesheet, followed by the initiation of interlaminar delamination between 45° ply and 0° ply, and meanwhile, the fracture of 45° ply, then the rapid propagation of interlaminar delamination between 45° ply and 0° ply, and finally, ending in the symmetrical global buckling of facesheets. Compared with the results of the end compressive test, the new failure mode predicted in the simulation is validated well in the experiment.
2007, 24(6): 128-134.
Abstract:
A stepping scheme was described for analyzing the effective properties of composites containing multiple kinds of inclusions with different shapes and sizes. In the stepping scheme the inclusions are treated kind by kind and the effective stiffness coefficients of the resultant composites in each step are calculated. Numerical results indicate that the stepping scheme can precisely deal with the problem with high volume fraction of inclusions and multiple inclusions. For the binary composites consisting of matrix and one kind of inclusion, the present result is in agreement with that of the differential scheme.
A stepping scheme was described for analyzing the effective properties of composites containing multiple kinds of inclusions with different shapes and sizes. In the stepping scheme the inclusions are treated kind by kind and the effective stiffness coefficients of the resultant composites in each step are calculated. Numerical results indicate that the stepping scheme can precisely deal with the problem with high volume fraction of inclusions and multiple inclusions. For the binary composites consisting of matrix and one kind of inclusion, the present result is in agreement with that of the differential scheme.
2007, 24(6): 135-139.
Abstract:
An effective calculational model was established to analyze delamination and fiber failure of composite laminates due to quasi-static pressure. The calculational model was based on the 3D progressive damage theory, which can simulate the whole process of the composite laminates failure due to quasi-static pressure. It could calculate and judge failure by each layer and each element, and predict the progressive damage process under increasing load for any layer orientation angle and thickness. The prediction of delamination and fiber failure phenomenon of carbon fiber/epoxy resin laminates as well as delamination and ultimate failure contact force of carbon fiber/bismaleimide resin laminates was made by using this model, and compared with the experiment results. Good agreement between calculational results and experimental results was obtained, which proves that the quasi-static indentation (QSI) is an alternative analysis of low-velocity impact.
An effective calculational model was established to analyze delamination and fiber failure of composite laminates due to quasi-static pressure. The calculational model was based on the 3D progressive damage theory, which can simulate the whole process of the composite laminates failure due to quasi-static pressure. It could calculate and judge failure by each layer and each element, and predict the progressive damage process under increasing load for any layer orientation angle and thickness. The prediction of delamination and fiber failure phenomenon of carbon fiber/epoxy resin laminates as well as delamination and ultimate failure contact force of carbon fiber/bismaleimide resin laminates was made by using this model, and compared with the experiment results. Good agreement between calculational results and experimental results was obtained, which proves that the quasi-static indentation (QSI) is an alternative analysis of low-velocity impact.
2007, 24(6): 140-146.
Abstract:
A series experiments were carried out to investigate the responses of X-Z-pinned foam core sandwich materials under shear loading, including inclination angles of 15° and 25° with foam core thickness of 12.7mm and 8mm, each group of which had a contrasted one. The experimental results show that the Z-pinned foam core can reinforce the shear modulus and strength of the sandwich markedly. At the same time, the X-Z-pin reinforced material has a special failure pattern which is different from the unreinforced one. On the basis of integrating the space truss frame and equivalent inclusion method, a method for predicting the shear modulus of the composites was established. The theoretical prediction coincides with the experimental data well. In addition, the novel Z-pinned cores are found to exhibit more favorable programmable property than the conventional sandwich cores. Altering the pinned angle and pin materials can ameliorate the mechanical properties of sandwich.
A series experiments were carried out to investigate the responses of X-Z-pinned foam core sandwich materials under shear loading, including inclination angles of 15° and 25° with foam core thickness of 12.7mm and 8mm, each group of which had a contrasted one. The experimental results show that the Z-pinned foam core can reinforce the shear modulus and strength of the sandwich markedly. At the same time, the X-Z-pin reinforced material has a special failure pattern which is different from the unreinforced one. On the basis of integrating the space truss frame and equivalent inclusion method, a method for predicting the shear modulus of the composites was established. The theoretical prediction coincides with the experimental data well. In addition, the novel Z-pinned cores are found to exhibit more favorable programmable property than the conventional sandwich cores. Altering the pinned angle and pin materials can ameliorate the mechanical properties of sandwich.
2007, 24(6): 147-152.
Abstract:
In terms of the characteristic of temperature field, a precise finite element model (FEM) was established for the sandwich composite structure. The FEM was a 3D hexahedral model. A variety of properties between structure layers was considered in the established FEM. The interpolation function that the value of the function was continuous but the derivative of the function was not continuous at the interface node of layers was chosen to be the field function of the established finite element for the direction of thickness. The corresponding heat transfer FEM equation based on the presented element was also obtained. In terms of the characteristic of the nonlinear ordinary differential heat transfer FEM equation that the thermal property of the material is affected by temperature, the dynamical equation solution was improved. The improved methods will avoid iteration in each time step in the solution process. The numerical example will show the efficiency and reliability of the present method.
In terms of the characteristic of temperature field, a precise finite element model (FEM) was established for the sandwich composite structure. The FEM was a 3D hexahedral model. A variety of properties between structure layers was considered in the established FEM. The interpolation function that the value of the function was continuous but the derivative of the function was not continuous at the interface node of layers was chosen to be the field function of the established finite element for the direction of thickness. The corresponding heat transfer FEM equation based on the presented element was also obtained. In terms of the characteristic of the nonlinear ordinary differential heat transfer FEM equation that the thermal property of the material is affected by temperature, the dynamical equation solution was improved. The improved methods will avoid iteration in each time step in the solution process. The numerical example will show the efficiency and reliability of the present method.
2007, 24(6): 153-159.
Abstract:
In the molding process of fiber reinforced polymeric material, the flow residual stress caused by fibers impacts the performance of material seriously. The analysis of flow residual stress depends on the proper model which must include information of different scales. Here, a multi-scale model was used, in which the macro-flow, the mesoscopic fiber orientation and the microscopic polymer molecular chains were coupled together. In a contraction cavity, using the SIMPLER-FDMS (Semi-implicit method for pressure linked equations revised and finite difference method on source term) method, the fiber orientation and stress distribution of the fiber reinforced polymeric melt were analyzed. And the normal stress difference and shear stress of polymeric melt coupled with fibers or not were discussed. The results show that the fibers rotate periodically in the zone where the shearing motion is dominant, and the fibers orientate along a single axis in the stretched zone; as the fibers rotate periodically, the normal stress difference distribution of fiber reinforced polymeric melt appears unsteady coherent vortex configuration.
In the molding process of fiber reinforced polymeric material, the flow residual stress caused by fibers impacts the performance of material seriously. The analysis of flow residual stress depends on the proper model which must include information of different scales. Here, a multi-scale model was used, in which the macro-flow, the mesoscopic fiber orientation and the microscopic polymer molecular chains were coupled together. In a contraction cavity, using the SIMPLER-FDMS (Semi-implicit method for pressure linked equations revised and finite difference method on source term) method, the fiber orientation and stress distribution of the fiber reinforced polymeric melt were analyzed. And the normal stress difference and shear stress of polymeric melt coupled with fibers or not were discussed. The results show that the fibers rotate periodically in the zone where the shearing motion is dominant, and the fibers orientate along a single axis in the stretched zone; as the fibers rotate periodically, the normal stress difference distribution of fiber reinforced polymeric melt appears unsteady coherent vortex configuration.
2007, 24(6): 160-165.
Abstract:
A hybrid numerical method was proposed for the analysis of transient responses subjected to coupled electro-mechanical loads in piezoelectric laminates. The displacement and electro-potential fields were discretized in the thickness direction of the laminates. The governing equations were determined by the coupled electroelastic theory and Hamilton principle. The modal analysis and Fourier transformation were introduced to formulate the displacement and electro-potential field in the wave-number domain. The transient responses were obtained by employing the inverse Fourier transformation. The results of the numerical example provide the transient responses excited by the coupled electro-mechanical line load in a PZT-5A/0° PVDF composite plate. The dynamic characteristics of this type of piezoelectric laminates are described. The finite element method, the Fourier transformation and modal analysis are effectively combined in the present method. Much fewer elements are needed especially for analyzing the transient responses excited by loads with high frequency. The present method is flexible to deal with piezoelectric laminates consisting of any type of piezoelectric materials excited by any electro-mechanical loads.
A hybrid numerical method was proposed for the analysis of transient responses subjected to coupled electro-mechanical loads in piezoelectric laminates. The displacement and electro-potential fields were discretized in the thickness direction of the laminates. The governing equations were determined by the coupled electroelastic theory and Hamilton principle. The modal analysis and Fourier transformation were introduced to formulate the displacement and electro-potential field in the wave-number domain. The transient responses were obtained by employing the inverse Fourier transformation. The results of the numerical example provide the transient responses excited by the coupled electro-mechanical line load in a PZT-5A/0° PVDF composite plate. The dynamic characteristics of this type of piezoelectric laminates are described. The finite element method, the Fourier transformation and modal analysis are effectively combined in the present method. Much fewer elements are needed especially for analyzing the transient responses excited by loads with high frequency. The present method is flexible to deal with piezoelectric laminates consisting of any type of piezoelectric materials excited by any electro-mechanical loads.
2007, 24(6): 166-172.
Abstract:
Based on the Donnels shell theory, the creep buckling behavior, in the form of limit point, was investigated for viscoelastic laminated circular cylindrical shells under uniformly axial compression with geometrical imperfections. The quasi-elastic approach was applied to the analysis of end-shorting following elapsed time, and the critical time is determined at which the snap-through of end-shorting occurs. The numerical investigation of glass/epoxy laminated circular cylindrical shells was performed. It is shown that there exist durable critical loads which correspond to infinite critical time. The difference between transient critical load and durable critical load, which characterizes the extent of time-dependent buckling, decreases with the increase of imperfection. The mechanism of the influence on the buckling behavior for ply mode, the amplitude of imperfection and boundary conditions as well can be examined by combining the discussion on the sensitivity of imperfection for the corresponding elastic counterpart.
Based on the Donnels shell theory, the creep buckling behavior, in the form of limit point, was investigated for viscoelastic laminated circular cylindrical shells under uniformly axial compression with geometrical imperfections. The quasi-elastic approach was applied to the analysis of end-shorting following elapsed time, and the critical time is determined at which the snap-through of end-shorting occurs. The numerical investigation of glass/epoxy laminated circular cylindrical shells was performed. It is shown that there exist durable critical loads which correspond to infinite critical time. The difference between transient critical load and durable critical load, which characterizes the extent of time-dependent buckling, decreases with the increase of imperfection. The mechanism of the influence on the buckling behavior for ply mode, the amplitude of imperfection and boundary conditions as well can be examined by combining the discussion on the sensitivity of imperfection for the corresponding elastic counterpart.
Barycentric finite element method for predicting the effective elastic moduli of composite materials
2007, 24(6): 173-179.
Abstract:
Applying a geometrical method to construct the shape functions of the polygonal element, a barycentric finite element method (BFEM) for solving elastic problems was presented. The effective moduli in the transverse section of SiC/Ti and B/Al fiber composites were simulated numerically by BFEM. The computational modeling of BFEM was isotropic hexagonal representative unit cell in the transverse section of the material. The Youngs moduli, shear moduli and the bulk moduli were simulated numerically using BFEM and FEM in a wide range of volume fractions. The effective moduli in BFEM computation are in good agreement with the analytical prediction and the FEM results. In contrast to the FEM, the shapes of the elements in BFEM can be arbitrary polygons with the number of sides larger than four. So BFEM can realize the numerical simulation based on real mesostructure of the composite materials. The numerical examples demonstrate that the BFEM has higher computational efficiency and accuracy.
Applying a geometrical method to construct the shape functions of the polygonal element, a barycentric finite element method (BFEM) for solving elastic problems was presented. The effective moduli in the transverse section of SiC/Ti and B/Al fiber composites were simulated numerically by BFEM. The computational modeling of BFEM was isotropic hexagonal representative unit cell in the transverse section of the material. The Youngs moduli, shear moduli and the bulk moduli were simulated numerically using BFEM and FEM in a wide range of volume fractions. The effective moduli in BFEM computation are in good agreement with the analytical prediction and the FEM results. In contrast to the FEM, the shapes of the elements in BFEM can be arbitrary polygons with the number of sides larger than four. So BFEM can realize the numerical simulation based on real mesostructure of the composite materials. The numerical examples demonstrate that the BFEM has higher computational efficiency and accuracy.
2007, 24(6): 180-184.
Abstract:
Based on the software of ANSYS, an APDL code was programmed in which a progressive damage model was established to simulate the failure and the behavior of in-plane woven composite laminates numerically. In the model Hanshin criteria and Reddy stiffness attenuation methods which fit for uni-directional lamina were modified for in-plane fabrics. The experimental researches were carried out on G803/5224 laminates and laminates with a hole to verify this model. The simulating results with this model are coordinate with the test results very well. This method is relatively simple and intuitional when it is used to estimate the damage propagation and residual tensile strength. It would provide a numerical method for the analysis of the damage propagation and tensile failure of woven composite laminates, which is suitable for engineering application.
Based on the software of ANSYS, an APDL code was programmed in which a progressive damage model was established to simulate the failure and the behavior of in-plane woven composite laminates numerically. In the model Hanshin criteria and Reddy stiffness attenuation methods which fit for uni-directional lamina were modified for in-plane fabrics. The experimental researches were carried out on G803/5224 laminates and laminates with a hole to verify this model. The simulating results with this model are coordinate with the test results very well. This method is relatively simple and intuitional when it is used to estimate the damage propagation and residual tensile strength. It would provide a numerical method for the analysis of the damage propagation and tensile failure of woven composite laminates, which is suitable for engineering application.
