2014 Vol. 31, No. 4
2014, 31(4): 859-865.
Abstract:
Based on the Particle-Filler model (P-F) and Langmuir-Hinshelwood mechanism of pyrocarbon deposition, a multistep heterogeneous reaction kinetic mechanism including adsorption/desorption/dehydrogenation reactions was proposed, by which continuous deposition of pyrocarbon on surface of the carbon fiber in the preparation of carbon/carbon composites and the formation process of texture interface were theoretically modeled. Then a Gibbs ensemble Monte Carlo (MC) method was used to simulate the pyrocarbon texture formation in chemical vapor infiltration (CVI) process. This study shows that P-F bimolecular reaction happening on the surface of deposition will be restricted due to the fact that the adsorption of the light aromatic component in gas phase represented by C6 is more likely to be suppressed, compared to the adsorption of the light linear hydrocarbons represented by C2. With the change of the concentration ratio R of C6 to C2 component, the texture formation process of pyrocarbon exhibits bi-stability distribution leading to the formation of two different metastable phases, i.e. medium-textured (MT) and high-textured (HT) pyrocarbons. And a sharp texture interface appears in the pyrocarbon of the carbon/carbon composites. The further simulation results indicate that the bistable transition of pyrocarbon textures is accompanied by a hysteresis cross domain, which is affected by the composition parameter R of gas phase, initial concentration of light linear hydrocarbons C2 and deposition temperature T. CVI process parameters have to be selected outside the range of hysteresis cross domain to produce pyrocarbon with a pure composition.
Based on the Particle-Filler model (P-F) and Langmuir-Hinshelwood mechanism of pyrocarbon deposition, a multistep heterogeneous reaction kinetic mechanism including adsorption/desorption/dehydrogenation reactions was proposed, by which continuous deposition of pyrocarbon on surface of the carbon fiber in the preparation of carbon/carbon composites and the formation process of texture interface were theoretically modeled. Then a Gibbs ensemble Monte Carlo (MC) method was used to simulate the pyrocarbon texture formation in chemical vapor infiltration (CVI) process. This study shows that P-F bimolecular reaction happening on the surface of deposition will be restricted due to the fact that the adsorption of the light aromatic component in gas phase represented by C6 is more likely to be suppressed, compared to the adsorption of the light linear hydrocarbons represented by C2. With the change of the concentration ratio R of C6 to C2 component, the texture formation process of pyrocarbon exhibits bi-stability distribution leading to the formation of two different metastable phases, i.e. medium-textured (MT) and high-textured (HT) pyrocarbons. And a sharp texture interface appears in the pyrocarbon of the carbon/carbon composites. The further simulation results indicate that the bistable transition of pyrocarbon textures is accompanied by a hysteresis cross domain, which is affected by the composition parameter R of gas phase, initial concentration of light linear hydrocarbons C2 and deposition temperature T. CVI process parameters have to be selected outside the range of hysteresis cross domain to produce pyrocarbon with a pure composition.
2014, 31(4): 866-872.
Abstract:
The functionalized multi-walled carbon nanotubes (MWCNTs) webs (buckypaper) were prepared by using positive pressure filtering process, and the functionalized MWCNTs webs were impregnated with epoxy by vacuum assistant RTM process. The morphology and performance of the MWCNTs webs were examined with SEM, FTIR and tensile testing methods. The mechanical properties of the MWCNTs web/epoxy composites were also measured by using tensile test. The results show that the functionalized MWCNTs webs is homogeneous, tensile strength is between 22 and 32 MPa, tensile modulus is around 1 GPa. The tensile strength is improved by 167% compared with that of the un-functionalized MWCNTs web. The strength and modulus of the functionalized MWCNTs webs/epoxy composites can reach 152 MPa and 6.48 GPa, respectively, improved by 100% compared with that of the neat epoxy. The fractured surfaces of some typical specimens from SEM observation show that the webs are impregnated well with epoxy and the interfacial bonding between the MWCNTs webs and epoxy matrix are good, which leads to the improvement of the mechanical properties of the composites.
The functionalized multi-walled carbon nanotubes (MWCNTs) webs (buckypaper) were prepared by using positive pressure filtering process, and the functionalized MWCNTs webs were impregnated with epoxy by vacuum assistant RTM process. The morphology and performance of the MWCNTs webs were examined with SEM, FTIR and tensile testing methods. The mechanical properties of the MWCNTs web/epoxy composites were also measured by using tensile test. The results show that the functionalized MWCNTs webs is homogeneous, tensile strength is between 22 and 32 MPa, tensile modulus is around 1 GPa. The tensile strength is improved by 167% compared with that of the un-functionalized MWCNTs web. The strength and modulus of the functionalized MWCNTs webs/epoxy composites can reach 152 MPa and 6.48 GPa, respectively, improved by 100% compared with that of the neat epoxy. The fractured surfaces of some typical specimens from SEM observation show that the webs are impregnated well with epoxy and the interfacial bonding between the MWCNTs webs and epoxy matrix are good, which leads to the improvement of the mechanical properties of the composites.
2014, 31(4): 873-879.
Abstract:
In order to improve the mechanical properties of phenolic foam(PF), phenolic foam composites reinforced by hollow glass beads (HGB) were prepared by compression molding. The compressive property and thermal stability of the composites were evaluated by mechanics performance test, TG analysis and vertical burning method, and the strengthen mechanism were also analyzed. The results show that when the mass ratio of HGB to PF reaches 10%, both of the compressive strength and compressive modulus of PF/HGB reach the maximum value. Pretreated with silicane coupling agent, the compressive strength and compressive modulus of hollow glass beads reinforced phenolic foams improve substantially. TG analysis and vertical burning method show that HGB as filler reduces thermal degradation rate of foam, leading to slightly higher thermal stability but slightly lower flame resistance. Analyses by SEM, FTIR and EDS reveal that the breakage behavior of PF/HGB is breakage of the cells, which leads to the HGB debond or rigid fracture. The froth density of PF/HGB increases, frothy diameter decreases, the interfacial adhesion between the surface of hollow glass bead and PF matrix is good, and hollow glass beads disperse homogeneously in PF matrix.
In order to improve the mechanical properties of phenolic foam(PF), phenolic foam composites reinforced by hollow glass beads (HGB) were prepared by compression molding. The compressive property and thermal stability of the composites were evaluated by mechanics performance test, TG analysis and vertical burning method, and the strengthen mechanism were also analyzed. The results show that when the mass ratio of HGB to PF reaches 10%, both of the compressive strength and compressive modulus of PF/HGB reach the maximum value. Pretreated with silicane coupling agent, the compressive strength and compressive modulus of hollow glass beads reinforced phenolic foams improve substantially. TG analysis and vertical burning method show that HGB as filler reduces thermal degradation rate of foam, leading to slightly higher thermal stability but slightly lower flame resistance. Analyses by SEM, FTIR and EDS reveal that the breakage behavior of PF/HGB is breakage of the cells, which leads to the HGB debond or rigid fracture. The froth density of PF/HGB increases, frothy diameter decreases, the interfacial adhesion between the surface of hollow glass bead and PF matrix is good, and hollow glass beads disperse homogeneously in PF matrix.
2014, 31(4): 880-887.
Abstract:
Polyvinylidene fluoride (PVDF) based composites filled with insulating BaTiO3, semiconductive SiC and conductive graphite nanoplatelet (GNP) were fabricated by simple solution mixing process. The effects of different nanofillers on the dielectric behavior of PVDF-based composites were mainly investigated. The results show that the dielectric constant of PVDF-based composites is found to increase with the increasing of all nanofiller contents, particularly for the composites with semiconductive SiC and conductive GNP fillers. The dielectric relaxation behavior of SiC/PVDF and GNP/PVDF composites can also be verified via ε'-ε" plot, where the relaxation peaks of PVDF-based composites at high frequency region tend to be straight when the content of SiC and GNP reaches the percolation threshold. In addition, the form of dielectric modulus can well describe the relaxation behavior of the PVDF-based composites. The relaxation activation energy reduces with the increasing of nanofiller content, which indicates that the addition of the nanofiller improves the polarization of PVDF-based composites.
Polyvinylidene fluoride (PVDF) based composites filled with insulating BaTiO3, semiconductive SiC and conductive graphite nanoplatelet (GNP) were fabricated by simple solution mixing process. The effects of different nanofillers on the dielectric behavior of PVDF-based composites were mainly investigated. The results show that the dielectric constant of PVDF-based composites is found to increase with the increasing of all nanofiller contents, particularly for the composites with semiconductive SiC and conductive GNP fillers. The dielectric relaxation behavior of SiC/PVDF and GNP/PVDF composites can also be verified via ε'-ε" plot, where the relaxation peaks of PVDF-based composites at high frequency region tend to be straight when the content of SiC and GNP reaches the percolation threshold. In addition, the form of dielectric modulus can well describe the relaxation behavior of the PVDF-based composites. The relaxation activation energy reduces with the increasing of nanofiller content, which indicates that the addition of the nanofiller improves the polarization of PVDF-based composites.
2014, 31(4): 888-894.
Abstract:
Fiber/resin composites need a good interface, so that the load can effectively pass from matrix to reinforced fiber, fiber surface modification is the main way to achieve this requirement. The method of hydrochloric acid etching the fiber surface of basalt fiber (BF) was adopted. The effects of acid etching on the monofilament tensile strength, adsorption amount of silane coupling agent on fiber surface were studied, and the effects of hydrochloric acid concentration on the mechanical property of BF/epoxy composites were discussed. The results demonstrate that with the increasing of HCl concentration, the monofilament tensile strength of fiber shows a trend of accelerated decline. The fiber etched by 1 mol/L HCl has more surface adsorption quantity of silane coupling agent KH550. The BF-KH550/epoxy composites pretreated by 1 mol/L HCl and silane coupling agent KH550 have relatively greater mechanical properties in bending performance, tensile properties and interlaminar shear strength.
Fiber/resin composites need a good interface, so that the load can effectively pass from matrix to reinforced fiber, fiber surface modification is the main way to achieve this requirement. The method of hydrochloric acid etching the fiber surface of basalt fiber (BF) was adopted. The effects of acid etching on the monofilament tensile strength, adsorption amount of silane coupling agent on fiber surface were studied, and the effects of hydrochloric acid concentration on the mechanical property of BF/epoxy composites were discussed. The results demonstrate that with the increasing of HCl concentration, the monofilament tensile strength of fiber shows a trend of accelerated decline. The fiber etched by 1 mol/L HCl has more surface adsorption quantity of silane coupling agent KH550. The BF-KH550/epoxy composites pretreated by 1 mol/L HCl and silane coupling agent KH550 have relatively greater mechanical properties in bending performance, tensile properties and interlaminar shear strength.
2014, 31(4): 895-901.
Abstract:
To prepare one kind of composites with excellent mechanical properties, which would be used in long load-bearing bone repairing, different contents of quartz fiber (QF )with mass ratio of 30wt% and 45wt% were used to enhance polyamide-46 (PA46) and QF/PA46 composites were prepared by extrusion and injection molding. The structure, interface, mechanical performance and nonisothermal crystallization behavior of composites were studied by using burning test, FTIR, XRD, SEM and DSC. The results show that QF is uniformly distributed in composites and is quasi-isotropic. QF and PA46 matrix are mainly linked by hydrogen bond. The crystallinity of materials decreases with increasing QF contents. QF enhances the crystallization growth rate of PA46 and contributes to heterogeneous nucleating agent, but the interface action between QF and PA46 hinders the molecules' order arrangement, which decreases the crystallization degree. The crystallization peaks of PA46 and QF/PA46 move from higher temperature to lower with the increase of cooling rate, meanwhile, the width of crystallization peak becomes larger. The mechanical test indicates that more QF (within a certain limits) in composites leads to an increase in tensile strength and bending strength, which are close to those of the natural compact bone. The cytotoxicity test (adopting L929 fibroblast) shows that cytotoxicity level of the composites is grade 1, indicating it has a better biological safety. The QF/PA46 composites have potential application in long load-bearing bone repairing.
To prepare one kind of composites with excellent mechanical properties, which would be used in long load-bearing bone repairing, different contents of quartz fiber (QF )with mass ratio of 30wt% and 45wt% were used to enhance polyamide-46 (PA46) and QF/PA46 composites were prepared by extrusion and injection molding. The structure, interface, mechanical performance and nonisothermal crystallization behavior of composites were studied by using burning test, FTIR, XRD, SEM and DSC. The results show that QF is uniformly distributed in composites and is quasi-isotropic. QF and PA46 matrix are mainly linked by hydrogen bond. The crystallinity of materials decreases with increasing QF contents. QF enhances the crystallization growth rate of PA46 and contributes to heterogeneous nucleating agent, but the interface action between QF and PA46 hinders the molecules' order arrangement, which decreases the crystallization degree. The crystallization peaks of PA46 and QF/PA46 move from higher temperature to lower with the increase of cooling rate, meanwhile, the width of crystallization peak becomes larger. The mechanical test indicates that more QF (within a certain limits) in composites leads to an increase in tensile strength and bending strength, which are close to those of the natural compact bone. The cytotoxicity test (adopting L929 fibroblast) shows that cytotoxicity level of the composites is grade 1, indicating it has a better biological safety. The QF/PA46 composites have potential application in long load-bearing bone repairing.
2014, 31(4): 902-908.
Abstract:
Large amounts of recycled polyvinyl butyral (RPVB) are produced in China every year. Making full use of RPVB not only reduces the cost, but also plays an important role in energy saving, environmental protection and low carbon. In the present work, the natural sisal fibers were dewaxed and treated with alkaline, then microfibrillated with mechanical treatment, and the obtained sisal microfibrils (SMF) were finally made into a mat form. RPVB was crosslinked by glutaraldehyde (GTA) and sodium borate (SB). The SMF/crosslinked RPVB composites were prepared by solvent impregnation technique. The structure and properties of the composites were analyzed by using SEM, FTIR, TG and mechanical tests. The results show that alkaline-mechanical treatment can successfully separate natural sisal fibers with the diameter of 150-200 μm into microfibrils with the diameter of 5-10 μm and aspect ratio of length to diameter higher than 100. GTA and SB could successfully crosslink the RPVB, and the elongation at break of obtained composite films increases considerably. The interfacial adhesion of RPVB and SMF is good, however, the uniformity of the composites is not good enough, due to the fact that only part of the RPVB penetrates into the interior of sisal microfibril mat. The TG analysis shows that the thermal stability of SMF/RPVB composites is intermediate between RPVB and SMF.
Large amounts of recycled polyvinyl butyral (RPVB) are produced in China every year. Making full use of RPVB not only reduces the cost, but also plays an important role in energy saving, environmental protection and low carbon. In the present work, the natural sisal fibers were dewaxed and treated with alkaline, then microfibrillated with mechanical treatment, and the obtained sisal microfibrils (SMF) were finally made into a mat form. RPVB was crosslinked by glutaraldehyde (GTA) and sodium borate (SB). The SMF/crosslinked RPVB composites were prepared by solvent impregnation technique. The structure and properties of the composites were analyzed by using SEM, FTIR, TG and mechanical tests. The results show that alkaline-mechanical treatment can successfully separate natural sisal fibers with the diameter of 150-200 μm into microfibrils with the diameter of 5-10 μm and aspect ratio of length to diameter higher than 100. GTA and SB could successfully crosslink the RPVB, and the elongation at break of obtained composite films increases considerably. The interfacial adhesion of RPVB and SMF is good, however, the uniformity of the composites is not good enough, due to the fact that only part of the RPVB penetrates into the interior of sisal microfibril mat. The TG analysis shows that the thermal stability of SMF/RPVB composites is intermediate between RPVB and SMF.
2014, 31(4): 909-915.
Abstract:
In order to improve the water resistance and poor surface property of waterborne polyurethane (WPU), organosilicone and nano-SiO2 were introduced into the WPU. First, WPU and organosilicon modified waterborne polyurethane (SWPU) were synthesized by self-emulsified method. Then, nano-SiO2/SWPU composites were prepared by adding SiO2 particles into SWPU using ultrasonic blending method. Finally, the structures of WPU, SWPU and nano-SiO2/SWPU were characterized by FTIR and SEM, and their hydrophobicity and mechanical properties were analyzed by water contact angle measurement, water absorption and elongation mechanic test. Results show that nano-SiO2 is successfully introduced into SWPU. Nano-SiO2 could disperse uniformly in the film of nano-SiO2/SWPU when nano-SiO2 content is low (≤3wt%). When the content of nano-SiO2 increases from 0 to 5wt%, the water absorption of nano-SiO2/SWPU film decreases by 69%, the tensile strength increases from 16.72 MPa to 24.22 MPa, while the break elongation increases from 545% to 731%, which show that the introduction of nano-SiO2 significantly improves the water resistance and mechanical properties of SWPU.
In order to improve the water resistance and poor surface property of waterborne polyurethane (WPU), organosilicone and nano-SiO2 were introduced into the WPU. First, WPU and organosilicon modified waterborne polyurethane (SWPU) were synthesized by self-emulsified method. Then, nano-SiO2/SWPU composites were prepared by adding SiO2 particles into SWPU using ultrasonic blending method. Finally, the structures of WPU, SWPU and nano-SiO2/SWPU were characterized by FTIR and SEM, and their hydrophobicity and mechanical properties were analyzed by water contact angle measurement, water absorption and elongation mechanic test. Results show that nano-SiO2 is successfully introduced into SWPU. Nano-SiO2 could disperse uniformly in the film of nano-SiO2/SWPU when nano-SiO2 content is low (≤3wt%). When the content of nano-SiO2 increases from 0 to 5wt%, the water absorption of nano-SiO2/SWPU film decreases by 69%, the tensile strength increases from 16.72 MPa to 24.22 MPa, while the break elongation increases from 545% to 731%, which show that the introduction of nano-SiO2 significantly improves the water resistance and mechanical properties of SWPU.
2014, 31(4): 916-924.
Abstract:
The natural aging of glass fiber reinforced bromide epoxy vinyl ester composites was investigated in Wanning and Lasa stations of Chinese typical climate regions. Its accelerated aging experiments including hydrothermal, hot air, light and hot water were studied in laboratory at the same time. The mechanical properties including tensile strength, flexural strength, and compressive strength of glass fiber reinforced bromide epoxy vinyl ester composites after aging were tested. By using the grey correlation analysis method, the relationship between the natural aging and accelerated aging was calculated. The results show that the accelerated light aging has the best correlation with the natural aging, whose correlation degree reaches to 0.75 when taking compressive strength as property indicator. Accelerated factor (AF) and accelerated switch factor (ASF) between natural aging and accelerated light aging are obtained. The ultimate ASF in Lasa and Wanning is 5.28 and 7.25, respectively.
The natural aging of glass fiber reinforced bromide epoxy vinyl ester composites was investigated in Wanning and Lasa stations of Chinese typical climate regions. Its accelerated aging experiments including hydrothermal, hot air, light and hot water were studied in laboratory at the same time. The mechanical properties including tensile strength, flexural strength, and compressive strength of glass fiber reinforced bromide epoxy vinyl ester composites after aging were tested. By using the grey correlation analysis method, the relationship between the natural aging and accelerated aging was calculated. The results show that the accelerated light aging has the best correlation with the natural aging, whose correlation degree reaches to 0.75 when taking compressive strength as property indicator. Accelerated factor (AF) and accelerated switch factor (ASF) between natural aging and accelerated light aging are obtained. The ultimate ASF in Lasa and Wanning is 5.28 and 7.25, respectively.
2014, 31(4): 925-930.
Abstract:
In order to improve the properties of poly (butylene succinate) (PBS)-based composites and reduce the production cost of PBS-based composites, the wheat straw powder/PBS-poly (butylene adipate-co-terephthalate) (PBAT) composites were prepared by melt-blending method, and then the composites were irradiated by 60Co-γ rays. The effects of radiation modification on mechanical properties, thermal stability and thermal deformation temperature of wheat straw powder/PBS-PBAT composites were studied. FTIR and SEM were used to observe the structure and fracture surface morphology of the composites before and after the radiation treatment. Results show that when the triallyl isocyanurate (TAIC) content is 1wt% and the composites are irradiated by 30 kGy dose, the tensile strength, bending strength and impact strength are increased by 20%, 23.5% and 6.5% respectively. The pyrolysis rate of the composites is improved by radiation modification, its thermal deformation temperature rises by about 11℃, and the cohesiveness is strengthened between composite components.
In order to improve the properties of poly (butylene succinate) (PBS)-based composites and reduce the production cost of PBS-based composites, the wheat straw powder/PBS-poly (butylene adipate-co-terephthalate) (PBAT) composites were prepared by melt-blending method, and then the composites were irradiated by 60Co-γ rays. The effects of radiation modification on mechanical properties, thermal stability and thermal deformation temperature of wheat straw powder/PBS-PBAT composites were studied. FTIR and SEM were used to observe the structure and fracture surface morphology of the composites before and after the radiation treatment. Results show that when the triallyl isocyanurate (TAIC) content is 1wt% and the composites are irradiated by 30 kGy dose, the tensile strength, bending strength and impact strength are increased by 20%, 23.5% and 6.5% respectively. The pyrolysis rate of the composites is improved by radiation modification, its thermal deformation temperature rises by about 11℃, and the cohesiveness is strengthened between composite components.
2014, 31(4): 931-936.
Abstract:
Epoxy has excellent thermal and mechanical properties, but is brittle. Polyethersulphone(PES) and multi-walled carbon nanotubes(MWCNT) were used to toughen epoxy for the preparation of low cost and high performance epoxy system. PES-epoxy blends of different PES contents were prepared and the influence of PES content on mechanical properties of epoxy was discussed. MWCNT/PES-epoxy composites were prepared by using melting method with mechanical agitatioin, high-shearing agitation and ultrasonic dispersion. The tensile properties and fracture toughness were tested. Both the dispersion of MWCNT in resin and the fracture surfaces of broken specimens were observed by SEM. The results show that the comprehensive mechanical properties of PES-epoxy composites can be further improved by adding MWCNT and arrive at the highest value when the MWCNT content is 0.7wt%. At low PES content, the mechanical properties of epoxy with MWCNT content less than 1.0wt% can exceed that of epoxy with 20.0wt% PES. PES and MWCNT have synergistic toughening effects on epoxy.
Epoxy has excellent thermal and mechanical properties, but is brittle. Polyethersulphone(PES) and multi-walled carbon nanotubes(MWCNT) were used to toughen epoxy for the preparation of low cost and high performance epoxy system. PES-epoxy blends of different PES contents were prepared and the influence of PES content on mechanical properties of epoxy was discussed. MWCNT/PES-epoxy composites were prepared by using melting method with mechanical agitatioin, high-shearing agitation and ultrasonic dispersion. The tensile properties and fracture toughness were tested. Both the dispersion of MWCNT in resin and the fracture surfaces of broken specimens were observed by SEM. The results show that the comprehensive mechanical properties of PES-epoxy composites can be further improved by adding MWCNT and arrive at the highest value when the MWCNT content is 0.7wt%. At low PES content, the mechanical properties of epoxy with MWCNT content less than 1.0wt% can exceed that of epoxy with 20.0wt% PES. PES and MWCNT have synergistic toughening effects on epoxy.
2014, 31(4): 937-943.
Abstract:
In order to improve the processing flow performance of wood plastic composites (WPC), the capillary rheological properties of the wood flour/high density polyethylene (HDPE) composites modified by ionomer were studied by using a HAAKE Minilab rheometer. Results show that the wood flour/HDPE melts are all pesudoplastic fluid with or without ionomer, which all show the shear thinning effects. Both the shear stress and apparent viscosity of wood flour/HDPE modified by ionomer show the decline trends with the increasing of sodium ionomer and shear rate, which indicates the addition of sodium ionomer could improve the flowability of HDPE melts obviously. The shear stress and apparent viscosity of wood flour/HDPE adding 4wt% sodium ionomer and 4wt% zinc ionomer are both lower than those of the wood flour/HDPE composites adding 4wt% coupling agent maleic anhydride grafted polyethylene (MAH-g-PE), which demonstrates ionomer could improve the flowability of WPC melt much more compared with MAH-g-PE, and decrease the frictional resistance between HDPE and wood flour as melt flows. SEM analysis shows that HDPE polymer has a good coated effect on wood flour after being added ionomer without clear gap between wood flour and HDPE matrix. In addition, there exists a large number of fibrils on the fracture surface of WPC.
In order to improve the processing flow performance of wood plastic composites (WPC), the capillary rheological properties of the wood flour/high density polyethylene (HDPE) composites modified by ionomer were studied by using a HAAKE Minilab rheometer. Results show that the wood flour/HDPE melts are all pesudoplastic fluid with or without ionomer, which all show the shear thinning effects. Both the shear stress and apparent viscosity of wood flour/HDPE modified by ionomer show the decline trends with the increasing of sodium ionomer and shear rate, which indicates the addition of sodium ionomer could improve the flowability of HDPE melts obviously. The shear stress and apparent viscosity of wood flour/HDPE adding 4wt% sodium ionomer and 4wt% zinc ionomer are both lower than those of the wood flour/HDPE composites adding 4wt% coupling agent maleic anhydride grafted polyethylene (MAH-g-PE), which demonstrates ionomer could improve the flowability of WPC melt much more compared with MAH-g-PE, and decrease the frictional resistance between HDPE and wood flour as melt flows. SEM analysis shows that HDPE polymer has a good coated effect on wood flour after being added ionomer without clear gap between wood flour and HDPE matrix. In addition, there exists a large number of fibrils on the fracture surface of WPC.
2014, 31(4): 944-948.
Abstract:
In order to investigate the influence of hydrolyzed collagen (HC) and compatibilizer maleic anhydride grafted low density polyethylene (LDPE-g-MAH) on property of polymer materials, using low density polyethylene (LDPE) as the matrix, HC/LDPE and HC/LDPE-MAH composites were prepared by co-blend and extrusion method, then the samples of different specifications by injection molding were made. Through mechanical property test, SEM and thermal analysis, the effect of HC and LDPE-g-MAH content on morphology and properties of HC/LDPE, HC/LDPE-MAH were studied. Results show that when 5wt% of HC is added into the composites, the tensile strength of HC/LDPE composites reaches its maximum value 15.824 MPa. The addition of LDPE-g-MAH can improve the interface bonding, mechanical properties and thermal stability evidently, when 20wt% of HC and 4wt% of LDPE-g-MAH are added into the composites, HC/LDPE-MAH composites can obtain the optimal tensile performance.
In order to investigate the influence of hydrolyzed collagen (HC) and compatibilizer maleic anhydride grafted low density polyethylene (LDPE-g-MAH) on property of polymer materials, using low density polyethylene (LDPE) as the matrix, HC/LDPE and HC/LDPE-MAH composites were prepared by co-blend and extrusion method, then the samples of different specifications by injection molding were made. Through mechanical property test, SEM and thermal analysis, the effect of HC and LDPE-g-MAH content on morphology and properties of HC/LDPE, HC/LDPE-MAH were studied. Results show that when 5wt% of HC is added into the composites, the tensile strength of HC/LDPE composites reaches its maximum value 15.824 MPa. The addition of LDPE-g-MAH can improve the interface bonding, mechanical properties and thermal stability evidently, when 20wt% of HC and 4wt% of LDPE-g-MAH are added into the composites, HC/LDPE-MAH composites can obtain the optimal tensile performance.
2014, 31(4): 949-954.
Abstract:
The hole edge collapse defects in drilling medium and high volume ratio silicon carbide particle reinforced aluminum matrix composites (SiCp/Al) were observed by 3D test and statistically summarized, the defect mathematics model of edge collapse was established and a geometric method based on edge collapse volume has been presented to evaluate edge collapse level. The results show that the main defects in drilling SiCp/Al composites are edge collapse defects which are mainly produced at the exit of hole. The evaluation method is objective and real to evaluate the edge collapse defect level under different parameters in drilling SiCp/Al composites, and it has a certain guiding significance to process parameters optimization.
The hole edge collapse defects in drilling medium and high volume ratio silicon carbide particle reinforced aluminum matrix composites (SiCp/Al) were observed by 3D test and statistically summarized, the defect mathematics model of edge collapse was established and a geometric method based on edge collapse volume has been presented to evaluate edge collapse level. The results show that the main defects in drilling SiCp/Al composites are edge collapse defects which are mainly produced at the exit of hole. The evaluation method is objective and real to evaluate the edge collapse defect level under different parameters in drilling SiCp/Al composites, and it has a certain guiding significance to process parameters optimization.
2014, 31(4): 955-962.
Abstract:
Interface has great influence on the creep properties of composites. A theoretical analysis model was established for aluminum silicate short fiber reinforced AZ91D magnesium matrix composites on the basis of test analysis, and by using 3D finite element analysis method, the effects of interface properties, stress and strain distribution on the interface and short fiber orientation change on the creep properties of aluminum silicate short fiber reinforced AZ91D magnesium matrix composites were systematically investigated. The research shows that the interface properties such as thickness and modulus, have effects on the maximum fiber axial stress and steady-state creep rate. The maximum fiber axial stress decreases with the increasing of interface thickness, and increases with the increasing of interface modulus. The steady-state creep rate increases with the increasing of interface thickness, and decreases with the increasing of interface modulus. Both remain unchanged when the interface modulus is bigger than the matrix modulus. The short fiber orientation also affects the distribution of the axial stress and steady-state creep rate. There is a greater stress and strain on the interface of the fiber end where microcracks are easily produced, which decreases the creep resistance of the material. The interface can affect creep curves and creep fracture mechanism of aluminum silicate short fiber reinforced AZ91D magnesium matrix composites, and the impact is also related with short fiber orientation.
Interface has great influence on the creep properties of composites. A theoretical analysis model was established for aluminum silicate short fiber reinforced AZ91D magnesium matrix composites on the basis of test analysis, and by using 3D finite element analysis method, the effects of interface properties, stress and strain distribution on the interface and short fiber orientation change on the creep properties of aluminum silicate short fiber reinforced AZ91D magnesium matrix composites were systematically investigated. The research shows that the interface properties such as thickness and modulus, have effects on the maximum fiber axial stress and steady-state creep rate. The maximum fiber axial stress decreases with the increasing of interface thickness, and increases with the increasing of interface modulus. The steady-state creep rate increases with the increasing of interface thickness, and decreases with the increasing of interface modulus. Both remain unchanged when the interface modulus is bigger than the matrix modulus. The short fiber orientation also affects the distribution of the axial stress and steady-state creep rate. There is a greater stress and strain on the interface of the fiber end where microcracks are easily produced, which decreases the creep resistance of the material. The interface can affect creep curves and creep fracture mechanism of aluminum silicate short fiber reinforced AZ91D magnesium matrix composites, and the impact is also related with short fiber orientation.
2014, 31(4): 963-969.
Abstract:
In order to determine the dynamic recrystallization behavior of TiC/Cu-Al2O3 composites and provide theoretical reference for the development of hot working process parameters. Using the Gleeble-1500D simulator, the hot simulation compression tests of TiC/Cu-Al2O3 composites were conducted at deformation temperature of 450-850℃, the strain rate of 0.001-1 s-1 and total strain of 0.7. The true stress-strain curves of TiC/Cu-Al2O3 composites were fitted and analyzed. The work hardening rate of TiC/Cu-Al2O3 composites was obtained. The critical conditions of dynamic recrystallization were studied by the inflection point criterion of work hardening rate-strain curves and the minimum value criterion of corresponding partial derivative curves. The results indicate that the softening mechanism of the dynamic recrystallization is a feature of true stress-strain curves of the composites, and the peak stress increases with the decrease of deformation temperature or the increase of strain rate. The inflection point in the work hanrdening rate-strain curve appears and the minimum value of the corresponding partial derivative curve is presented when the critical state is attained for this composite. The critical strain decreases with the increasing deformation temperature and the decreasing strain rate. There is linear relationship between critical stra in, peak strain and Zener-Hollomon parameter.
In order to determine the dynamic recrystallization behavior of TiC/Cu-Al2O3 composites and provide theoretical reference for the development of hot working process parameters. Using the Gleeble-1500D simulator, the hot simulation compression tests of TiC/Cu-Al2O3 composites were conducted at deformation temperature of 450-850℃, the strain rate of 0.001-1 s-1 and total strain of 0.7. The true stress-strain curves of TiC/Cu-Al2O3 composites were fitted and analyzed. The work hardening rate of TiC/Cu-Al2O3 composites was obtained. The critical conditions of dynamic recrystallization were studied by the inflection point criterion of work hardening rate-strain curves and the minimum value criterion of corresponding partial derivative curves. The results indicate that the softening mechanism of the dynamic recrystallization is a feature of true stress-strain curves of the composites, and the peak stress increases with the decrease of deformation temperature or the increase of strain rate. The inflection point in the work hanrdening rate-strain curve appears and the minimum value of the corresponding partial derivative curve is presented when the critical state is attained for this composite. The critical strain decreases with the increasing deformation temperature and the decreasing strain rate. There is linear relationship between critical stra in, peak strain and Zener-Hollomon parameter.
2014, 31(4): 970-980.
Abstract:
Based on continuum damage mechanics(CDM) approach, a progressive damage model is proposed to predict the impact force and energy response of the carbon fiber-reinforced polymer (CFRP) laminates subjected to low velocity impact. The typical failure modes were simulated by employing damage mode-based failure criteria, irreversible damage variables and computing method of internal energy were defined in order to quantify damage associated with the gradual stiffness reduction and energy dissipation. A good agreement was found between the numerical simulation and experimental results. In addition, the difference between the Hashin criterion and LaRC04 criterion were analyzed, and a combined criterion composed of Hashin and LaRC04 criterion was advised for composite laminates subjected to low velocity impact. Comparison between the Hashin criterion and combined criterion indicates that when there is a lot of compressive failure damage in CFRP composite laminates, combined criterion is more suitable for the case in this paper, and a conservative result would be obtained if Hashin criterion is adopted.
Based on continuum damage mechanics(CDM) approach, a progressive damage model is proposed to predict the impact force and energy response of the carbon fiber-reinforced polymer (CFRP) laminates subjected to low velocity impact. The typical failure modes were simulated by employing damage mode-based failure criteria, irreversible damage variables and computing method of internal energy were defined in order to quantify damage associated with the gradual stiffness reduction and energy dissipation. A good agreement was found between the numerical simulation and experimental results. In addition, the difference between the Hashin criterion and LaRC04 criterion were analyzed, and a combined criterion composed of Hashin and LaRC04 criterion was advised for composite laminates subjected to low velocity impact. Comparison between the Hashin criterion and combined criterion indicates that when there is a lot of compressive failure damage in CFRP composite laminates, combined criterion is more suitable for the case in this paper, and a conservative result would be obtained if Hashin criterion is adopted.
2014, 31(4): 981-990.
Abstract:
According to the given configuration and dimension of composite wing model, the multilevel optimization method was used to determine the design scheme of wing. First, the efficiency evaluation of single factor and comprehensive efficiency evaluation of grey correlation degree were introduced to obtain the optimum wing layout. Then, the structure detail optimization of I-beam wing based on the finite element method and ply design were carried out. Finally, four kinds of typical composite wing models (i.e. skin-foam structure, skin-stiffened structure, front C-beam structure and I-beam structure) were manufactured by using integral forming process based on the method of vacuum bag. Then the three point bending test was used to verify the optimization design. The optimization results show that the I-beam wing has the highest structural efficiency, then followed by the back C-beam wing. The skin-web wing performs with the least structural efficiency. The flange can gain approximate equal strength beam by using constant thickness and variable width. The effectiveness of the optimization method was verified by the experimental results.
According to the given configuration and dimension of composite wing model, the multilevel optimization method was used to determine the design scheme of wing. First, the efficiency evaluation of single factor and comprehensive efficiency evaluation of grey correlation degree were introduced to obtain the optimum wing layout. Then, the structure detail optimization of I-beam wing based on the finite element method and ply design were carried out. Finally, four kinds of typical composite wing models (i.e. skin-foam structure, skin-stiffened structure, front C-beam structure and I-beam structure) were manufactured by using integral forming process based on the method of vacuum bag. Then the three point bending test was used to verify the optimization design. The optimization results show that the I-beam wing has the highest structural efficiency, then followed by the back C-beam wing. The skin-web wing performs with the least structural efficiency. The flange can gain approximate equal strength beam by using constant thickness and variable width. The effectiveness of the optimization method was verified by the experimental results.
2014, 31(4): 991-997.
Abstract:
As a new kind of variable angle tow (VAT) placement technology, continuous tow shearing (CTS) could significantly overcome process-induced defects in the traditional automated fiber placement (AFP). Taking the VAT laminates made by CTS and AFP respectively as research objects, the finite element analysis of their buckling property were carried out. Under the axial end shortening, based on the stack sequence[90±<0|75>]4s, the stress resultant distribution of CTS laminate and AFP laminate were compared. After that, the effect of minimum turning radius on these two placement technologies was demonstrated. The result shows that CTS laminate performs better than AFP laminate on buckling for its variable thickness character, and AFP's usage is restricted when the laminate dimension is small for the constraint of minimum turning radius, while CTS is suitable for all kinds of dimensions.
As a new kind of variable angle tow (VAT) placement technology, continuous tow shearing (CTS) could significantly overcome process-induced defects in the traditional automated fiber placement (AFP). Taking the VAT laminates made by CTS and AFP respectively as research objects, the finite element analysis of their buckling property were carried out. Under the axial end shortening, based on the stack sequence[90±<0|75>]4s, the stress resultant distribution of CTS laminate and AFP laminate were compared. After that, the effect of minimum turning radius on these two placement technologies was demonstrated. The result shows that CTS laminate performs better than AFP laminate on buckling for its variable thickness character, and AFP's usage is restricted when the laminate dimension is small for the constraint of minimum turning radius, while CTS is suitable for all kinds of dimensions.
2014, 31(4): 998-1005.
Abstract:
Based on the generalized self-consistent principle, the mechanical properties of syntactic foams under tensile loading were investigated by a four phase sphere model, and the possible damages happening in syntactic foams were analyzed. After degradation of the model, computational results show that the predicted strength values of foams agree with experimental results well. By analyzing the normal stress concentration coefficient of interface between microspheres and matrix and von Mises stress distribution of matrix, it is found that the mechanical behavior of microspheres is similar with flexible solid particles's as the wall of microspheres is very thin. With the increase in wall thickness of microspheres, the influence of microspheres on whole mechanical behavior of material accords with rigid solid particle's. Finally, through introducing the damage effect factors, prediction for the strength of the syntactic foams were studied and an effective method for prediction of strength was provided.
Based on the generalized self-consistent principle, the mechanical properties of syntactic foams under tensile loading were investigated by a four phase sphere model, and the possible damages happening in syntactic foams were analyzed. After degradation of the model, computational results show that the predicted strength values of foams agree with experimental results well. By analyzing the normal stress concentration coefficient of interface between microspheres and matrix and von Mises stress distribution of matrix, it is found that the mechanical behavior of microspheres is similar with flexible solid particles's as the wall of microspheres is very thin. With the increase in wall thickness of microspheres, the influence of microspheres on whole mechanical behavior of material accords with rigid solid particle's. Finally, through introducing the damage effect factors, prediction for the strength of the syntactic foams were studied and an effective method for prediction of strength was provided.
2014, 31(4): 1006-1012.
Abstract:
The variation of residual stress and strain in filament-wound composites with metal liner during curing process was simulated using the finite element analysis software ABAQUS. A FORTRAN subroutine was developed to analyze the residual stress, in which the variation of mechanical parameters of composite and the chemical shrinkage strain during curing process were considered. The simulation results show that at initial stage, the residual stress of composite and metal liner is close to zero. And at a certain time of the curing process, the residual stress rapidly increases to the maximum value, and in the cooling stage, part of the residual stress decreases. In the curing process the metal liner is pressured while the filament-wound layer is stretched. Using the three-dimensional finite element model, the temperature and curing degree distribution of the composite can be obtained at any time of the curing process. The simulation method can be used to optimize the curing temperature cycle and improve the quality of filament-wound composite products.
The variation of residual stress and strain in filament-wound composites with metal liner during curing process was simulated using the finite element analysis software ABAQUS. A FORTRAN subroutine was developed to analyze the residual stress, in which the variation of mechanical parameters of composite and the chemical shrinkage strain during curing process were considered. The simulation results show that at initial stage, the residual stress of composite and metal liner is close to zero. And at a certain time of the curing process, the residual stress rapidly increases to the maximum value, and in the cooling stage, part of the residual stress decreases. In the curing process the metal liner is pressured while the filament-wound layer is stretched. Using the three-dimensional finite element model, the temperature and curing degree distribution of the composite can be obtained at any time of the curing process. The simulation method can be used to optimize the curing temperature cycle and improve the quality of filament-wound composite products.
2014, 31(4): 1013-1021.
Abstract:
Based on the viewpoint of progressive damage evolution with energy realease, a continuum damage mechanics (CDM) model, including damage description, damage initiation criterion and damage evolution law, was proposed for intralaminar failure analysis of composite laminates. Based on the CDM model, the damage constitutive of material in plane stress condition was established by introducing damage state variables which characterize corresponding damage. The damage initiation was estimated by using rewritten Hashin's criteria, which was expressed with damage parameter fE. The damage evolution was controlled by the density of strain energy release within the characteristic length. The progressive damage evolution law associating damage state variables with equivalent strain was established. Intralaminar shear nonlinearity and mesh sensitivity were also taken into accounts in the model and analyzed comparatively. Failure analysis of notched[90/0/±45]3s and[(±θ)4]s composite laminates under intralaminar tensile load was implemented, and the result shows that the present model is capable of predicting the intralaminar tensile strength of composite laminates.
Based on the viewpoint of progressive damage evolution with energy realease, a continuum damage mechanics (CDM) model, including damage description, damage initiation criterion and damage evolution law, was proposed for intralaminar failure analysis of composite laminates. Based on the CDM model, the damage constitutive of material in plane stress condition was established by introducing damage state variables which characterize corresponding damage. The damage initiation was estimated by using rewritten Hashin's criteria, which was expressed with damage parameter fE. The damage evolution was controlled by the density of strain energy release within the characteristic length. The progressive damage evolution law associating damage state variables with equivalent strain was established. Intralaminar shear nonlinearity and mesh sensitivity were also taken into accounts in the model and analyzed comparatively. Failure analysis of notched[90/0/±45]3s and[(±θ)4]s composite laminates under intralaminar tensile load was implemented, and the result shows that the present model is capable of predicting the intralaminar tensile strength of composite laminates.
2014, 31(4): 1022-1029.
Abstract:
In order to realize the optimization of process parameters within a certain tolerance of drilling defects, the organization structure of the composites was tested to obtain the sectional morphologies and feature size of composite laminates by SEM. Then the orthogonal experiment was designed to test the thrust and torque, and the delamination, tearing and roundness error arising from drilling process were measured. The mechanism of defects was analyzed. The relevant variation was studied from the measured value by non-linear fitting. The relationships between the drilling defects and the thrust force, torque deviation were established to obtain the critical range respectively. At last, the spindle speed, feed rate and chisel edge eccentricity coefficient were selected as decision variables, and reaching the maximum material removal rate was chosen as the optimization goal, and the defects tolerance of drilling were selected as the constraint condition. And the parameter optimization model of drilling was established. The optimization of process parameters was realized with the MATLAB software to obtain the process parameters that ensure the maximum productivity and the suitable quality of composite drilling.
In order to realize the optimization of process parameters within a certain tolerance of drilling defects, the organization structure of the composites was tested to obtain the sectional morphologies and feature size of composite laminates by SEM. Then the orthogonal experiment was designed to test the thrust and torque, and the delamination, tearing and roundness error arising from drilling process were measured. The mechanism of defects was analyzed. The relevant variation was studied from the measured value by non-linear fitting. The relationships between the drilling defects and the thrust force, torque deviation were established to obtain the critical range respectively. At last, the spindle speed, feed rate and chisel edge eccentricity coefficient were selected as decision variables, and reaching the maximum material removal rate was chosen as the optimization goal, and the defects tolerance of drilling were selected as the constraint condition. And the parameter optimization model of drilling was established. The optimization of process parameters was realized with the MATLAB software to obtain the process parameters that ensure the maximum productivity and the suitable quality of composite drilling.
2014, 31(4): 1030-1036.
Abstract:
For low elastic modulus of bamboo, insufficient cross-sectional stiffness and bamboo fiber feasible fracture in tension zone of bamboo flexural components, bamboo structure reinforced with bars and its manufacturing processes were presented. Four bamboo scrimber flexural specimens were studied by four-point bending test. The failure modes and load carrying characteristics of the reinforced bamboo components were investigated. The test parameters include the types and the cross-sectional area of reinforced bars. The results show that the load carrying capacity and section stiffness of the reinforced specimens increase significantly. Specimens reinforced with steel bars gain higher the sectional stiffness than those with fiber reinfored polymer (FRP) bars. Due to the effects of reinforced bars, the compress plastic behavior of bamboo can develop fully, and the reinforced specimens show more obvious plastic development process. Moreover, the top ultimate compressive strain and the bottom ultimate tensile strain of the reinforced specimens are significantly larger than the control specimen, and the cross-sectional strain distribution agrees with the plane section assumption. The strain comparison between internal bars and external bamboo in the same height shows that internal bars and bamboo can work well together. Bamboo structure reinforced with bars is a new structure to improve its work performance effectively.
For low elastic modulus of bamboo, insufficient cross-sectional stiffness and bamboo fiber feasible fracture in tension zone of bamboo flexural components, bamboo structure reinforced with bars and its manufacturing processes were presented. Four bamboo scrimber flexural specimens were studied by four-point bending test. The failure modes and load carrying characteristics of the reinforced bamboo components were investigated. The test parameters include the types and the cross-sectional area of reinforced bars. The results show that the load carrying capacity and section stiffness of the reinforced specimens increase significantly. Specimens reinforced with steel bars gain higher the sectional stiffness than those with fiber reinfored polymer (FRP) bars. Due to the effects of reinforced bars, the compress plastic behavior of bamboo can develop fully, and the reinforced specimens show more obvious plastic development process. Moreover, the top ultimate compressive strain and the bottom ultimate tensile strain of the reinforced specimens are significantly larger than the control specimen, and the cross-sectional strain distribution agrees with the plane section assumption. The strain comparison between internal bars and external bamboo in the same height shows that internal bars and bamboo can work well together. Bamboo structure reinforced with bars is a new structure to improve its work performance effectively.
2014, 31(4): 1037-1045.
Abstract:
Equivalent inclusion method is a convenient tool for modeling the stress field of materials embedded with inhomogeneities. However, its analytical applications are limited to elliptical shaped inhomogeneity cases. In this work, a new powerful and versatile numerical extension to the original equivalent inclusion method, called numerical equivalent inclusion method, was proposed. The fundamental theory of the numerical equivalent inclusion method was introduced, and an implementation method, conjugate gradient method, was presented to solve the linear equation group of the equivalency condition of the new method. The method can be applied to 2D inhomogeneity problems with arbitrary shape through a handy numerical discretization. Benchmark comparisons with the analytical results for an elliptical inhomogeneity model illustrated the accuracy of the proposed solution method. The efficiency and convergence of the numerical equivalent inclusion method were also discussed in detail, the results show that the proposed method implemented by conjugate gradient method has significant advantages in efficiency compared with that by Gaussian elimination method, and can maintain the accuracy of the results as well. A half-elliptical inhomogeneity model and a kind of zirconia/alumina coextruded composites were utilized to demonstrate the capability of the new method on solving arbitrarily shaped inhomogeneity problems.
Equivalent inclusion method is a convenient tool for modeling the stress field of materials embedded with inhomogeneities. However, its analytical applications are limited to elliptical shaped inhomogeneity cases. In this work, a new powerful and versatile numerical extension to the original equivalent inclusion method, called numerical equivalent inclusion method, was proposed. The fundamental theory of the numerical equivalent inclusion method was introduced, and an implementation method, conjugate gradient method, was presented to solve the linear equation group of the equivalency condition of the new method. The method can be applied to 2D inhomogeneity problems with arbitrary shape through a handy numerical discretization. Benchmark comparisons with the analytical results for an elliptical inhomogeneity model illustrated the accuracy of the proposed solution method. The efficiency and convergence of the numerical equivalent inclusion method were also discussed in detail, the results show that the proposed method implemented by conjugate gradient method has significant advantages in efficiency compared with that by Gaussian elimination method, and can maintain the accuracy of the results as well. A half-elliptical inhomogeneity model and a kind of zirconia/alumina coextruded composites were utilized to demonstrate the capability of the new method on solving arbitrarily shaped inhomogeneity problems.
2014, 31(4): 1046-1052.
Abstract:
The importance of the vacuum pressure in the VARI process system to the quality of molding was analyzed. In this paper, experiments were designed and conducted to investigate the effect of position and degree of vacuum leakage to the quality of the composite. Leakage sites were pre-installed before the inlet valve, after the outlet valve, and between the inlet valve and the outlet valve of the VARI process separately, and the leakage severity was controlled by the size of the leakage site. The test articles produced with different leakage sites and different leakage severities were examined on appearance evaluation, thickness test and ultrasonic defect detection. And the open hole compression performance of different test articles were tested. Provided that slight vacuum leakage is present in the system, the corresponding effect on the final quality of the composite article prepared by VARI process should be judged according to the leakage sites. Provided that serious vacuum leakage is present in the system, the final quality of the composite article prepared by VARI process will be seriously affect regardless of the leakage sites. The open hole compression (OHC) strength of VARI molded composite laminate plate and the porosity of the article have an inverse relationship.
The importance of the vacuum pressure in the VARI process system to the quality of molding was analyzed. In this paper, experiments were designed and conducted to investigate the effect of position and degree of vacuum leakage to the quality of the composite. Leakage sites were pre-installed before the inlet valve, after the outlet valve, and between the inlet valve and the outlet valve of the VARI process separately, and the leakage severity was controlled by the size of the leakage site. The test articles produced with different leakage sites and different leakage severities were examined on appearance evaluation, thickness test and ultrasonic defect detection. And the open hole compression performance of different test articles were tested. Provided that slight vacuum leakage is present in the system, the corresponding effect on the final quality of the composite article prepared by VARI process should be judged according to the leakage sites. Provided that serious vacuum leakage is present in the system, the final quality of the composite article prepared by VARI process will be seriously affect regardless of the leakage sites. The open hole compression (OHC) strength of VARI molded composite laminate plate and the porosity of the article have an inverse relationship.
2014, 31(4): 1053-1062.
Abstract:
In order to study stress transfer and damage evolution of single fiber composite in the process of unidirectional loading, a three-dimensional numerical analysis model of progressive damage process based on shear-lag model was established. The curves of single fiber composite progressive damage process, fiber segment, strain load and fiber axial stress distribution at the critical state are in good agreement with the test results in reference, which show that the model established in this paper could effectively simulate damage initiation, damage evolution and critical fracture state. The influences of constituent modulus and strength on damage process were also researched. The results show that increasing fiber modulus can speed up the damage process while maintaining constituent strength unchanged, and the increasing matrix and interfacial modulus have little effect on progressive damage process. Maintaining modulus of constituent materials and interfacial strength unchanged, with the increase of fiber strength, both the initial and critical strain load of single fiber composite progressive damage process increase, and the fiber breaking point at the critical state reduces.
In order to study stress transfer and damage evolution of single fiber composite in the process of unidirectional loading, a three-dimensional numerical analysis model of progressive damage process based on shear-lag model was established. The curves of single fiber composite progressive damage process, fiber segment, strain load and fiber axial stress distribution at the critical state are in good agreement with the test results in reference, which show that the model established in this paper could effectively simulate damage initiation, damage evolution and critical fracture state. The influences of constituent modulus and strength on damage process were also researched. The results show that increasing fiber modulus can speed up the damage process while maintaining constituent strength unchanged, and the increasing matrix and interfacial modulus have little effect on progressive damage process. Maintaining modulus of constituent materials and interfacial strength unchanged, with the increase of fiber strength, both the initial and critical strain load of single fiber composite progressive damage process increase, and the fiber breaking point at the critical state reduces.
2014, 31(4): 1063-1071.
Abstract:
To study the dynamic response of contact force and damage condition of composite sandwich structures with thin facesheets subject to impact load, specimens of different facesheet thicknesses were tested via dropping weight method at various levels of impact energy using two impactors of different mass. The damage of specimen after impact was measured. The results reveal that when the impact energy is relatively low, the maximum contact force is low and increases with the increase of impact energy, and it will be constant after it reaches the threshold value. The dent in the facesheet and slight delamination around the impact center are the major failure modes at low impact energy, and fiber fracture and penetration will emerge as the impact energy increases. The diameter of delamination area is about 1.2 times of the impactor when the facesheet is un-penetrated with impactor rebound, and in this case there is no plateau on the declining stage of contact force-time curve. While in the penetrated cases, the impactor does not rebound and the diameter of delamination area is about 1.8 times of the impactor, in this case, there is plateau on the declining stage of contact force-time curve. Besides, the bigger mass impactor will lead to longer contact duration and bigger dent depth under the same impact energy after the maximum contact force reaches the threshold value.
To study the dynamic response of contact force and damage condition of composite sandwich structures with thin facesheets subject to impact load, specimens of different facesheet thicknesses were tested via dropping weight method at various levels of impact energy using two impactors of different mass. The damage of specimen after impact was measured. The results reveal that when the impact energy is relatively low, the maximum contact force is low and increases with the increase of impact energy, and it will be constant after it reaches the threshold value. The dent in the facesheet and slight delamination around the impact center are the major failure modes at low impact energy, and fiber fracture and penetration will emerge as the impact energy increases. The diameter of delamination area is about 1.2 times of the impactor when the facesheet is un-penetrated with impactor rebound, and in this case there is no plateau on the declining stage of contact force-time curve. While in the penetrated cases, the impactor does not rebound and the diameter of delamination area is about 1.8 times of the impactor, in this case, there is plateau on the declining stage of contact force-time curve. Besides, the bigger mass impactor will lead to longer contact duration and bigger dent depth under the same impact energy after the maximum contact force reaches the threshold value.
2014, 31(4): 1072-1076.
Abstract:
The stringer-embedded honeycomb structure, which contains the advantages of both honeycomb structure and riveted structure, is an innovative structure improved from honeycomb. However, the relative research on load distribution and failure modes on this type of structure is inadequate. Depend on the largest aluminum honeycomb sandwich structure under researching, beam-reinforced laminate method was used for numerical simulation. Further to this, a full-size physical test was also designed. Good agreement has been achieved in the comparison between the numerical simulation and test, which verifies the beam-reinforced laminate method. This paper also investigated load distribution and failure modes of stringer-embedded honeycomb structure, and it can be regarded as a design reference for similar structure.
The stringer-embedded honeycomb structure, which contains the advantages of both honeycomb structure and riveted structure, is an innovative structure improved from honeycomb. However, the relative research on load distribution and failure modes on this type of structure is inadequate. Depend on the largest aluminum honeycomb sandwich structure under researching, beam-reinforced laminate method was used for numerical simulation. Further to this, a full-size physical test was also designed. Good agreement has been achieved in the comparison between the numerical simulation and test, which verifies the beam-reinforced laminate method. This paper also investigated load distribution and failure modes of stringer-embedded honeycomb structure, and it can be regarded as a design reference for similar structure.
2014, 31(4): 1077-1083.
Abstract:
Considering damages of matrix micro-cracks and fiber/matrix debonding, the thermal expansion/contraction theoretical model of fiber reinforced composite (FRC) was developed by using micro-mechanical method. In the model, differences of opening and closing conditions of micro-cracks in different orientations, both in matrix and fiber/matrix interface corresponding to heating and cooling and their effects on average coefficient of thermal expansion/contraction (CTE/CTC) were explored. The model has also taken the ununiformity of stresses in micro-scale into account. Micro finite element model was built to validate the theoretical model. The results reveal that CTE and CTC of damaged FRC are not identical and their discrepancy depends on damage modes. The matrix micro-crack damage could promote transverse CTE of FRC higher than nondestructive material's and decrease transverse CTC lower than nondestructive material's, however it has little effect on longitudinal CTE/CTC. Fiber/matrix interface debonding could bring notable reduction of longitudinal CTC, but be ignorable to transverse CTC.
Considering damages of matrix micro-cracks and fiber/matrix debonding, the thermal expansion/contraction theoretical model of fiber reinforced composite (FRC) was developed by using micro-mechanical method. In the model, differences of opening and closing conditions of micro-cracks in different orientations, both in matrix and fiber/matrix interface corresponding to heating and cooling and their effects on average coefficient of thermal expansion/contraction (CTE/CTC) were explored. The model has also taken the ununiformity of stresses in micro-scale into account. Micro finite element model was built to validate the theoretical model. The results reveal that CTE and CTC of damaged FRC are not identical and their discrepancy depends on damage modes. The matrix micro-crack damage could promote transverse CTE of FRC higher than nondestructive material's and decrease transverse CTC lower than nondestructive material's, however it has little effect on longitudinal CTE/CTC. Fiber/matrix interface debonding could bring notable reduction of longitudinal CTC, but be ignorable to transverse CTC.
2014, 31(4): 1084-1090.
Abstract:
The analytical procedure of filament wound composite pipe under axial tension was built up with finite element analysis (FEA), which adopted micro stiffness model and improved progressing damage method for displaying the influence of filament winding pattern on propagation of damage in filament wound composite and its failure. The axial tensile experiments were performed for three kinds of winding pattern such as one, three and five represent volume element along the circumferential direction of filament wound composite pipe and failure model, average tensile strength and regulation of strength with winding pattern were obtained. The experiments show that the tensile failure of filament wound composite pipe under axial tension is mainly function failure with loss of bearing capacity. Winding pattern has some effect on the tensile strength of filament wound composite. The numerical simulation demonstrates that main damage are matrix crack and fiber/matrix debonding and fiber crossing can result in damage initiation and propagation more easily in the process of axial tension.
The analytical procedure of filament wound composite pipe under axial tension was built up with finite element analysis (FEA), which adopted micro stiffness model and improved progressing damage method for displaying the influence of filament winding pattern on propagation of damage in filament wound composite and its failure. The axial tensile experiments were performed for three kinds of winding pattern such as one, three and five represent volume element along the circumferential direction of filament wound composite pipe and failure model, average tensile strength and regulation of strength with winding pattern were obtained. The experiments show that the tensile failure of filament wound composite pipe under axial tension is mainly function failure with loss of bearing capacity. Winding pattern has some effect on the tensile strength of filament wound composite. The numerical simulation demonstrates that main damage are matrix crack and fiber/matrix debonding and fiber crossing can result in damage initiation and propagation more easily in the process of axial tension.
2014, 31(4): 1091-1097.
Abstract:
A three-phase moisture diffusion approach of composites was developed based upon the Halpin & Tsais model by analogizing the governing equations and boundary conditions of moisture diffusion and heat conduction. In this approach, the moisture diffusion effect of fiber/matrix inter-phase was taken into account. Three types of micro-scale FE models, i.e. hexagonally, randomly packed fibers and randomly distributed inter-phase damage, were built to valid the theoretical model. The predictions from theoretical approach and FE models are in good agreements under the conditions of various volume fractions, diffusivities of fiber and inter-phase as well as randomness of inter-phase damage. Critical inter-phase and fiber moisture diffusivities, independent on fiber volume fraction, are found in this study. When the inter-phase or fiber diffusivity is less than the critical value, the transverse effective moisture diffusivity of unidirectional composite(TEMDUC) will decrease with the increase of fiber volume fraction. On the contrary, the trend is opposite. Also, the fluctuation range of composites' effective moisture diffusivities is found narrow with the change of inter-phase damage distribution if the damage ratio has been given.
A three-phase moisture diffusion approach of composites was developed based upon the Halpin & Tsais model by analogizing the governing equations and boundary conditions of moisture diffusion and heat conduction. In this approach, the moisture diffusion effect of fiber/matrix inter-phase was taken into account. Three types of micro-scale FE models, i.e. hexagonally, randomly packed fibers and randomly distributed inter-phase damage, were built to valid the theoretical model. The predictions from theoretical approach and FE models are in good agreements under the conditions of various volume fractions, diffusivities of fiber and inter-phase as well as randomness of inter-phase damage. Critical inter-phase and fiber moisture diffusivities, independent on fiber volume fraction, are found in this study. When the inter-phase or fiber diffusivity is less than the critical value, the transverse effective moisture diffusivity of unidirectional composite(TEMDUC) will decrease with the increase of fiber volume fraction. On the contrary, the trend is opposite. Also, the fluctuation range of composites' effective moisture diffusivities is found narrow with the change of inter-phase damage distribution if the damage ratio has been given.
2014, 31(4): 1098-1105.
Abstract:
The hybrid modified industrial lignin (OMIL-PEI) consisting of industrial lignin oxidatively modified by H2O2 (OMIL) and polyethylenimine (PEI) was prepared. Using wood fiber (WF) as the matrix and OMIL-PEI as natural binder, the green OMIL-PEI/WF composites were prepared by the method of high speed mixed-flat of hot pressing. The orthogonal theories were used to analyze the effect of H2O2 dosage, oxidative time, mass ratio of OMIL to PEI and OMIL-PEI dosage on the mechanical properties and optimize the process parameters. The structure and property of the composites were analyzed by FTIR, XRD, DMA and SEM. Results show the optimum conditions are as follows: H2O2 dosage is 20wt%, oxidative time is 120 min, mass ratio of OMIL to PEI is 7:1 and OMIL-PEI dosage is 20wt%. The mechanical properties of OMIL-PEI/WF composites meet the mechanical property requirements of load bearing medium density fiberboard in dry state according to GB/T 11718-2009. The wood fiber gets a good chemical bond with OMIL-PEI. The crystalline structure of lignocellulose is not changed in OMIL-PEI/WF composites under the optimum conditions. The relative crystallinity increases from 60.24% for pure wood fiber to 72.91% for OMIL-PEI/WF composites. OMIL-PEI improves the dynamic storage modulus of OMIL-PEI/WF composites, but has not much effect on the thermostability of OMIL-PEI/WF composites. OMIL-PEI/WF composites has a good interfacial bondability with uniform mixtures.
The hybrid modified industrial lignin (OMIL-PEI) consisting of industrial lignin oxidatively modified by H2O2 (OMIL) and polyethylenimine (PEI) was prepared. Using wood fiber (WF) as the matrix and OMIL-PEI as natural binder, the green OMIL-PEI/WF composites were prepared by the method of high speed mixed-flat of hot pressing. The orthogonal theories were used to analyze the effect of H2O2 dosage, oxidative time, mass ratio of OMIL to PEI and OMIL-PEI dosage on the mechanical properties and optimize the process parameters. The structure and property of the composites were analyzed by FTIR, XRD, DMA and SEM. Results show the optimum conditions are as follows: H2O2 dosage is 20wt%, oxidative time is 120 min, mass ratio of OMIL to PEI is 7:1 and OMIL-PEI dosage is 20wt%. The mechanical properties of OMIL-PEI/WF composites meet the mechanical property requirements of load bearing medium density fiberboard in dry state according to GB/T 11718-2009. The wood fiber gets a good chemical bond with OMIL-PEI. The crystalline structure of lignocellulose is not changed in OMIL-PEI/WF composites under the optimum conditions. The relative crystallinity increases from 60.24% for pure wood fiber to 72.91% for OMIL-PEI/WF composites. OMIL-PEI improves the dynamic storage modulus of OMIL-PEI/WF composites, but has not much effect on the thermostability of OMIL-PEI/WF composites. OMIL-PEI/WF composites has a good interfacial bondability with uniform mixtures.
2014, 31(4): 1106-1111.
Abstract:
This paper provides a method of preparing tricalcium phosphate/calcium alginate (TCP/CA) composite flat sheet membranes to improve the strength of CA hydrogels, and make it easy to test the mechanical properties. The TCP/CA composite flat sheet membranes were prepared by combining TCP with sodium alginate in aqueous solution. The TCP/CA membranes were characterized by FTIR and SEM. The swelling properties and mechanical properties in wet and dry forms of TCP/CA membranes with different contents of TCP were investigated. The results show that with the increase of TCP, the swelling rate of TCP/CA composite flat sheet membranes decreases in physiological saline and the nominal stress value increases first and then decreases both in dry and wet forms with the increase of TCP content. The nominal stress, modulus and fracture energy are significantly greater in the dry form than in the wet form. This method is easy to get TCP/CA composite flat sheet membranes with different thicknesses and get mass production, which could be used in controlled-release delivery and tissue engineering.
This paper provides a method of preparing tricalcium phosphate/calcium alginate (TCP/CA) composite flat sheet membranes to improve the strength of CA hydrogels, and make it easy to test the mechanical properties. The TCP/CA composite flat sheet membranes were prepared by combining TCP with sodium alginate in aqueous solution. The TCP/CA membranes were characterized by FTIR and SEM. The swelling properties and mechanical properties in wet and dry forms of TCP/CA membranes with different contents of TCP were investigated. The results show that with the increase of TCP, the swelling rate of TCP/CA composite flat sheet membranes decreases in physiological saline and the nominal stress value increases first and then decreases both in dry and wet forms with the increase of TCP content. The nominal stress, modulus and fracture energy are significantly greater in the dry form than in the wet form. This method is easy to get TCP/CA composite flat sheet membranes with different thicknesses and get mass production, which could be used in controlled-release delivery and tissue engineering.
2014, 31(4): 1112-1116.
Abstract:
The imprinting modified magnetic crosslinking chitosan(Pb-TMCS)was prepared to improve the removal ability of chitosan (CS) to Pb2+, whose structure and morphology were characterized by FTIR, SEM and XRD, and the adsorption, desorption performance and selectivity of Pb2+ on Pb-TMCS were studied. Results show that compared with CS, Pb-TMCS has more pore and fold, and more -OH and-NH2 are introduced. The magnetic material Fe3O4 is embed in Pb-TMCS. The relative selectivity coefficient of Pb-TMCS to CS is more than 2. Pb-TMCS shows higher adsorption capacity (45.26 mg/g) than CS (25.57 mg/g) for Pb2+. Pb-TMCS could be used repeatedly after being desorpted 3 times. Recycling of Pb-TMCS is convenient, and it has high selective adsorption for Pb2+, and it is non-polluting, so it has good application prospect in treatment of heavy metal waste water.
The imprinting modified magnetic crosslinking chitosan(Pb-TMCS)was prepared to improve the removal ability of chitosan (CS) to Pb2+, whose structure and morphology were characterized by FTIR, SEM and XRD, and the adsorption, desorption performance and selectivity of Pb2+ on Pb-TMCS were studied. Results show that compared with CS, Pb-TMCS has more pore and fold, and more -OH and-NH2 are introduced. The magnetic material Fe3O4 is embed in Pb-TMCS. The relative selectivity coefficient of Pb-TMCS to CS is more than 2. Pb-TMCS shows higher adsorption capacity (45.26 mg/g) than CS (25.57 mg/g) for Pb2+. Pb-TMCS could be used repeatedly after being desorpted 3 times. Recycling of Pb-TMCS is convenient, and it has high selective adsorption for Pb2+, and it is non-polluting, so it has good application prospect in treatment of heavy metal waste water.
2014, 31(4): 1117-1120.
Abstract:
In order to improve corrosion resistance of polyaniline (PANI) film, in the system of aniline-sulfuric acid electrolytic fluid, the electrochemical constant current method was adopted to prepare PANI film on surface of stainless steel. The effect of Zn2+ doping on corrosion resistance of PANI film prepared by electrochemical synthesis was studied using electrochemical measurement technology, SEM and XRD. Results show that Zn2+ doping can change the microstructure morphology of PANI film from irregular flake into fibrous. The alternating-current impedance of PANI film increases markedly after doping modification, the corrosion potential moves towards the positive direction, and the corrosion current decreases. The 10wt% HCl drop corrosion time of the PANI film with doped Zn2+ is 320 s, and no rust appears after neutral salt mist experiment for 48 h.
In order to improve corrosion resistance of polyaniline (PANI) film, in the system of aniline-sulfuric acid electrolytic fluid, the electrochemical constant current method was adopted to prepare PANI film on surface of stainless steel. The effect of Zn2+ doping on corrosion resistance of PANI film prepared by electrochemical synthesis was studied using electrochemical measurement technology, SEM and XRD. Results show that Zn2+ doping can change the microstructure morphology of PANI film from irregular flake into fibrous. The alternating-current impedance of PANI film increases markedly after doping modification, the corrosion potential moves towards the positive direction, and the corrosion current decreases. The 10wt% HCl drop corrosion time of the PANI film with doped Zn2+ is 320 s, and no rust appears after neutral salt mist experiment for 48 h.
2014, 31(4): 1121-1126.
Abstract:
For detecting the toxic vapors in atmosphere, the homogeneous solution was prepared with nature cotton fiber and chitosan in 1-butyl-3-methylimidazolium chloride ([BMIm]Cl) ionic liquid. The multiwall carbon nanotubes (MWCNTs) with sodium dodecyl sulfate (SDS) modification were used as the conductve fillers. And MWCNTs/cellulose-chitosan conducting composites used for gas sensor were successfully prepared by using solution coating method. Results show that when the mass ratio of chitosan to cellulose is 1:7, MWCNTs/cellulose-chitosan composites show better gas-sensing properties, reproducibility and stability for polar organic solvent vapors methanol, ethanol, chloroform and acetone at percolation value of about 2.8wt%. The gas-sensing response behavior of MWCNTs/cellulose-chitosan composites shows typical negative vapor coefficient (NVC) effect.
For detecting the toxic vapors in atmosphere, the homogeneous solution was prepared with nature cotton fiber and chitosan in 1-butyl-3-methylimidazolium chloride ([BMIm]Cl) ionic liquid. The multiwall carbon nanotubes (MWCNTs) with sodium dodecyl sulfate (SDS) modification were used as the conductve fillers. And MWCNTs/cellulose-chitosan conducting composites used for gas sensor were successfully prepared by using solution coating method. Results show that when the mass ratio of chitosan to cellulose is 1:7, MWCNTs/cellulose-chitosan composites show better gas-sensing properties, reproducibility and stability for polar organic solvent vapors methanol, ethanol, chloroform and acetone at percolation value of about 2.8wt%. The gas-sensing response behavior of MWCNTs/cellulose-chitosan composites shows typical negative vapor coefficient (NVC) effect.
