2013 Vol. 30, No. 5
2013, 30(5): 1-8.
Abstract:
Antioxidant functionalized silica was designed and prepared from N-phenyl-1, 4-phenylenediamine(PPDA), (3-Glycidyloxypropyl)trimethoxysilane and silica to improve the dispersion of silica in the rubber matrix and to avoid the volatility and extractability of the antioxidants. The reinforcement and antioxidation effects of the modified silica in natural rubber (NR) were studied and compared with those of carbon black/NR, neat silica/NR and Si69 modified silica/NR (the latter three composites added with N-(1, 3-dimethylbutyl)-N-phenyl-1, 4-phenylenediamine (4020) as antioxidant). The results show that the use of antioxidant functionalized silica can prolong the scorch time, shorten the optimum curing time, improve the dispersion of silica in NR network, and improve the mechanical properties of the composites. The tensile strength and tear strength of the antioxidant functionalized silica/NR increase with increasing PPDA grafting content. When the PPDA content reaches 5.27% (mass fraction to silica), its tensile strength increases 90% and 73% to those of the neat silica/NR and Si69 modified silica/NR, respectively, and is closed to that of the carbon black/NR; its tear strength is 5, 2.5 and 2 times of those of neat silica/NR, Si69 modified silica/NR and carbon black/NR, respectively. Furthermore, the antioxidant functionalized silica/NR composites show great resistance in thermal oxidative ageing and damp heat ageing. Their stability is improved in ozone ageing compared with those used 4020 as antioxidant.
Antioxidant functionalized silica was designed and prepared from N-phenyl-1, 4-phenylenediamine(PPDA), (3-Glycidyloxypropyl)trimethoxysilane and silica to improve the dispersion of silica in the rubber matrix and to avoid the volatility and extractability of the antioxidants. The reinforcement and antioxidation effects of the modified silica in natural rubber (NR) were studied and compared with those of carbon black/NR, neat silica/NR and Si69 modified silica/NR (the latter three composites added with N-(1, 3-dimethylbutyl)-N-phenyl-1, 4-phenylenediamine (4020) as antioxidant). The results show that the use of antioxidant functionalized silica can prolong the scorch time, shorten the optimum curing time, improve the dispersion of silica in NR network, and improve the mechanical properties of the composites. The tensile strength and tear strength of the antioxidant functionalized silica/NR increase with increasing PPDA grafting content. When the PPDA content reaches 5.27% (mass fraction to silica), its tensile strength increases 90% and 73% to those of the neat silica/NR and Si69 modified silica/NR, respectively, and is closed to that of the carbon black/NR; its tear strength is 5, 2.5 and 2 times of those of neat silica/NR, Si69 modified silica/NR and carbon black/NR, respectively. Furthermore, the antioxidant functionalized silica/NR composites show great resistance in thermal oxidative ageing and damp heat ageing. Their stability is improved in ozone ageing compared with those used 4020 as antioxidant.
2013, 30(5): 9-13.
Abstract:
The nonlinear characteristic of the conductive rubber filled by carbon black used for pressure/temperature sensor was analyzed by the impact of the strain and resistivity on the negative pressure coefficient of resistance(NPCR) and the positive temperature coefficient of resistance(PTCR). It concludes that nonlinear change of resistivity has a great impact on the nonlinear characteristic of NPCR and PTCR. When the volume fraction of carbon black is close to the critical volume fraction, the resistivity is highly sensitive to the change of the volume of composite, and the nonlinear characteristic of NPCR and PTCR is strong. Because the compression coefficient is larger than the expansion coefficient and the deformation process of conductive barbon black/rubber under pressure and temperature is different, the nonlinear characteristic of NPCR is stronger than PTCR.
The nonlinear characteristic of the conductive rubber filled by carbon black used for pressure/temperature sensor was analyzed by the impact of the strain and resistivity on the negative pressure coefficient of resistance(NPCR) and the positive temperature coefficient of resistance(PTCR). It concludes that nonlinear change of resistivity has a great impact on the nonlinear characteristic of NPCR and PTCR. When the volume fraction of carbon black is close to the critical volume fraction, the resistivity is highly sensitive to the change of the volume of composite, and the nonlinear characteristic of NPCR and PTCR is strong. Because the compression coefficient is larger than the expansion coefficient and the deformation process of conductive barbon black/rubber under pressure and temperature is different, the nonlinear characteristic of NPCR is stronger than PTCR.
2013, 30(5): 14-20.
Abstract:
The fabrication, microstructure, compressive property and thermal performances of the phenolic foam reinforced with carboxyl carbon nanotubes(CNT-COOH) were studied. The reinforcement mechanism of CNT-COOH was investigated by analyzing FTIR and detailed failure behavior of 0.05%(mass fraction) CNT-COOH/phenolic foam composite and phenolic foam under different compressive strains. It is found that serving as the site of heterogeneous nucleation, CNT-COOH increases the cell density and decreases the cell size of the produced foams, and that CNT-COOH reinforced foams are evidently stiffer and stronger than the corresponding neat system as the increment of CNT-COOH content. FTIR reveals that curing reaction of CNT-COOH and phenolic resin may not exist. SEM analysis of the composite foams in different compressive strains reveals that adding CNT-COOH located in the cell walls could endure a certain load through the interface between CNT-COOH and phenolic resin, thereby enhancing the compressive strength of CNT-COOH/phenolic foam composites. In addition, thermogravimetric analysis (TGA) and vertical burning method show that CNT-COOH as stabilizer, reduces thermal degradation rate, leading to slightly higher thermal stability and resistance to flame of the foam composites.
The fabrication, microstructure, compressive property and thermal performances of the phenolic foam reinforced with carboxyl carbon nanotubes(CNT-COOH) were studied. The reinforcement mechanism of CNT-COOH was investigated by analyzing FTIR and detailed failure behavior of 0.05%(mass fraction) CNT-COOH/phenolic foam composite and phenolic foam under different compressive strains. It is found that serving as the site of heterogeneous nucleation, CNT-COOH increases the cell density and decreases the cell size of the produced foams, and that CNT-COOH reinforced foams are evidently stiffer and stronger than the corresponding neat system as the increment of CNT-COOH content. FTIR reveals that curing reaction of CNT-COOH and phenolic resin may not exist. SEM analysis of the composite foams in different compressive strains reveals that adding CNT-COOH located in the cell walls could endure a certain load through the interface between CNT-COOH and phenolic resin, thereby enhancing the compressive strength of CNT-COOH/phenolic foam composites. In addition, thermogravimetric analysis (TGA) and vertical burning method show that CNT-COOH as stabilizer, reduces thermal degradation rate, leading to slightly higher thermal stability and resistance to flame of the foam composites.
2013, 30(5): 21-28.
Abstract:
Sisal fibers with surface treatments, including potassium permanganate, sodium hydroxide, flame retardant agent, silane, and without treatment were investigated. The tensile properties and interfacial shear strength (IFSS) of sisal fiber with modified acrylate and epoxy resin were tested by using single fiber tensile method and micro-droplet debonding method, respectively. The effect of water absorption on the sisal fiber surface morphologies, the tensile properties and its interfacial adhesion were analyzed, and the corresponding fracture mode as well. The results show that after chemical treatments the tensile strength and modulus of sisal fibers are decreased to varying degrees. Compared with the untreated sisal fiber, the tensile strengths of potassium permanganate and silane treated fibers both decrease by 44%, the strength of sodium hydroxide treated fiber decreases by 27%, while that of flame retardant treated fiber is almost equivalent. The chemical treatments can decrease the IFSS of sisal fiber/modified acrylate and the decreasing degrees are different from those of the fiber tensile properties, in which lowest IFSS is found for flame retardant sisal fiber/modified acrylate with 2.0 MPa, decreasing by 80% in comparison with the untreated fiber system. After silane treatment, the water absorption rate is decreased, and the property retention rate is higher for the sisal fiber than those of the untreated fiber. For the hygrometric state sisal fiber/epoxy, the untreated fiber system shows IFSS of 6.6 MPa, higher than the silane treated fiber system. The fracture morphologies indicate that silane treatment tends to reduce the bonding of the inter-fibrils, thereby decreasing the sisal fiber tensile and interfacial properties with resin.
Sisal fibers with surface treatments, including potassium permanganate, sodium hydroxide, flame retardant agent, silane, and without treatment were investigated. The tensile properties and interfacial shear strength (IFSS) of sisal fiber with modified acrylate and epoxy resin were tested by using single fiber tensile method and micro-droplet debonding method, respectively. The effect of water absorption on the sisal fiber surface morphologies, the tensile properties and its interfacial adhesion were analyzed, and the corresponding fracture mode as well. The results show that after chemical treatments the tensile strength and modulus of sisal fibers are decreased to varying degrees. Compared with the untreated sisal fiber, the tensile strengths of potassium permanganate and silane treated fibers both decrease by 44%, the strength of sodium hydroxide treated fiber decreases by 27%, while that of flame retardant treated fiber is almost equivalent. The chemical treatments can decrease the IFSS of sisal fiber/modified acrylate and the decreasing degrees are different from those of the fiber tensile properties, in which lowest IFSS is found for flame retardant sisal fiber/modified acrylate with 2.0 MPa, decreasing by 80% in comparison with the untreated fiber system. After silane treatment, the water absorption rate is decreased, and the property retention rate is higher for the sisal fiber than those of the untreated fiber. For the hygrometric state sisal fiber/epoxy, the untreated fiber system shows IFSS of 6.6 MPa, higher than the silane treated fiber system. The fracture morphologies indicate that silane treatment tends to reduce the bonding of the inter-fibrils, thereby decreasing the sisal fiber tensile and interfacial properties with resin.
2013, 30(5): 29-33.
Abstract:
With the ultrasonic assistance, octamethylcyclotetrasiloxane(D4)and a little of silane coupling agent γ-(2, 3-epoxypropoxy) propyltrimethoxysilane (KH560) were sufficiently mixed with silica sol and the in-situ ring-opening polymerization of D4 and co-condensation with KH560 on the surface of silica nanoparticles, catalyzed by dodecylbenzene sulfonic acid (DBSA), were enhanced as well. The polydimethylsiloxane (PDMS) modified silica was obtained. The PDMS-modified silica sol was dispersed in the mixed monomers of methylmethacrylate (MMA) and butylmethacrylate (BA). Then miniemulsion polymerizations of the acrylate monomers containing PDMS-modified silica sol were carried out, with PDMS as hydrophobe to inhibit the Ostwald ripening of the monomer droplets and neutralized DBSA as emulsifier, both preexisted in the PDMS-modified silica sol. The SiO2/polyacrylates composite latex was obtained via miniemulsion polymerization. FTIR, TGA, TEM, Malvern Nanosizer and water contact angle tests were utilized to characterize the modified silica and the composite latex. The results show that silica is grafted and encapsulated by PDMS and KH560 with chemical bonds and is well dispersed in monomers, and the generated PDMS improves the hydrophobicity of the film of nanocomposite latex. The average size of nanocomposite particles with a (multi)core-shell structures is 98 nm when the silica mass fraction is 3% of the monomers.
With the ultrasonic assistance, octamethylcyclotetrasiloxane(D4)and a little of silane coupling agent γ-(2, 3-epoxypropoxy) propyltrimethoxysilane (KH560) were sufficiently mixed with silica sol and the in-situ ring-opening polymerization of D4 and co-condensation with KH560 on the surface of silica nanoparticles, catalyzed by dodecylbenzene sulfonic acid (DBSA), were enhanced as well. The polydimethylsiloxane (PDMS) modified silica was obtained. The PDMS-modified silica sol was dispersed in the mixed monomers of methylmethacrylate (MMA) and butylmethacrylate (BA). Then miniemulsion polymerizations of the acrylate monomers containing PDMS-modified silica sol were carried out, with PDMS as hydrophobe to inhibit the Ostwald ripening of the monomer droplets and neutralized DBSA as emulsifier, both preexisted in the PDMS-modified silica sol. The SiO2/polyacrylates composite latex was obtained via miniemulsion polymerization. FTIR, TGA, TEM, Malvern Nanosizer and water contact angle tests were utilized to characterize the modified silica and the composite latex. The results show that silica is grafted and encapsulated by PDMS and KH560 with chemical bonds and is well dispersed in monomers, and the generated PDMS improves the hydrophobicity of the film of nanocomposite latex. The average size of nanocomposite particles with a (multi)core-shell structures is 98 nm when the silica mass fraction is 3% of the monomers.
2013, 30(5): 34-40.
Abstract:
Ion-exchange polymer metal composites with silver as electrodes (Ag-IPMC) samples were manufactured by the chemical deposition method under different deposition temperatures and modification temperatures of 25℃-25℃, 15℃-25℃, 15℃-15℃, 10℃-10℃, 7.5℃-15℃ and 7.5℃-7.5℃. The topographies of chemical composition of the surface electrodes were analyzed. The tensile experiments and dynamic displacement tests of Ag-IPMC samples were taken. The results show that the diameters of Ag aggregations outside of the exchange membrane are smaller under lower temperature among the manufacturing temperature range of 7.5℃ to 25℃. Comparing the samples manufactured at reaction temperature of 7.5℃-7.5℃ to those manufactured at 25℃-25℃, the diameters of Ag particles are decreased by 60%. Electrode thickness of Ag-IPMC is affected deeply by temperature, the thicknesses of the surface and interlocked electrodes differ obviously (interlocked: ~130%, surface: ~70%). The sample with the maximum elastic modulus is prepared under 15℃-15℃, 28% larger than the minimum value. Within the experimental temperature range, the maximum driven deformation increases as the reaction temperature being lower, and the maximum value is 80% larger than the minimum.
Ion-exchange polymer metal composites with silver as electrodes (Ag-IPMC) samples were manufactured by the chemical deposition method under different deposition temperatures and modification temperatures of 25℃-25℃, 15℃-25℃, 15℃-15℃, 10℃-10℃, 7.5℃-15℃ and 7.5℃-7.5℃. The topographies of chemical composition of the surface electrodes were analyzed. The tensile experiments and dynamic displacement tests of Ag-IPMC samples were taken. The results show that the diameters of Ag aggregations outside of the exchange membrane are smaller under lower temperature among the manufacturing temperature range of 7.5℃ to 25℃. Comparing the samples manufactured at reaction temperature of 7.5℃-7.5℃ to those manufactured at 25℃-25℃, the diameters of Ag particles are decreased by 60%. Electrode thickness of Ag-IPMC is affected deeply by temperature, the thicknesses of the surface and interlocked electrodes differ obviously (interlocked: ~130%, surface: ~70%). The sample with the maximum elastic modulus is prepared under 15℃-15℃, 28% larger than the minimum value. Within the experimental temperature range, the maximum driven deformation increases as the reaction temperature being lower, and the maximum value is 80% larger than the minimum.
2013, 30(5): 41-47.
Abstract:
A series of nano antimony tin oxide (ATO)/polyvinyl butyral (PVB) composites were prepared using condensation reaction of polyvinyl alcohol (PVA) and butyraldehyde(BA) by in-situ method through dispersing the surface pretreated ATO in PVA solution with supersonic vibration. The structure, micro-morphology and properties of the nano-ATO/PVB composites were studied by using FTIR, UV/VIS/NIR (ultraviolet-visible-near infrared spectrophotometry), TG, TEM, AFM (atomic force microscope) and some other means. The results show that, a few nano-ATO particles added before the synthesizing of PVB resin can be uniformly dispersed in the matrix of PVB. The transmittance of the composites in ultraviolet light and near infrared light decreases obviously, but the visible light transmittance decreases slowly. The UV-shielding and heat-insulation performances increase continuously with the increase of nano-ATO content. For the lower ATO content (mass ratio 2.76% to PVB), the mechanical properties especially the toughness of the in-situ composites are markedly improved, the elongation at break increases by 7.3 times compared with PVB matrix. With the ATO mass ratio 1.74% to PVB, the visible light transmittance of the composite is higher than 70%, the ultraviolet transmittance is less than 10%, the transmittance of near infrared radiation is lower than 28%, the thermal conductivity is 0.23 W(m·K)-1. The air temperature inside the box with the cover plate made of the ATO/PVB composites decreases by 5.5℃ compared with the PVB film without ATO, and the composite film also exhibits a good visible transmittance, excellent properties of UV-shielding and heat-insulation.
A series of nano antimony tin oxide (ATO)/polyvinyl butyral (PVB) composites were prepared using condensation reaction of polyvinyl alcohol (PVA) and butyraldehyde(BA) by in-situ method through dispersing the surface pretreated ATO in PVA solution with supersonic vibration. The structure, micro-morphology and properties of the nano-ATO/PVB composites were studied by using FTIR, UV/VIS/NIR (ultraviolet-visible-near infrared spectrophotometry), TG, TEM, AFM (atomic force microscope) and some other means. The results show that, a few nano-ATO particles added before the synthesizing of PVB resin can be uniformly dispersed in the matrix of PVB. The transmittance of the composites in ultraviolet light and near infrared light decreases obviously, but the visible light transmittance decreases slowly. The UV-shielding and heat-insulation performances increase continuously with the increase of nano-ATO content. For the lower ATO content (mass ratio 2.76% to PVB), the mechanical properties especially the toughness of the in-situ composites are markedly improved, the elongation at break increases by 7.3 times compared with PVB matrix. With the ATO mass ratio 1.74% to PVB, the visible light transmittance of the composite is higher than 70%, the ultraviolet transmittance is less than 10%, the transmittance of near infrared radiation is lower than 28%, the thermal conductivity is 0.23 W(m·K)-1. The air temperature inside the box with the cover plate made of the ATO/PVB composites decreases by 5.5℃ compared with the PVB film without ATO, and the composite film also exhibits a good visible transmittance, excellent properties of UV-shielding and heat-insulation.
2013, 30(5): 49-54.
Abstract:
Electrorheological (ER) fluids were fabricated by dispersing oxalate group-modified amorphous titanium oxide nanoparticles in dimethyl silicone oil with different kinematic viscosities (10 cSt, 50 cSt, 100 cSt, 500 cSt and 1000 cSt). The yield stress, zero-field viscosity, ER efficiency, response time, and sedimentation stability were tested to find the influence of the viscosity of silicone oil on the properties of ER fluids. The results indicate that the ER fluids based on the silicone oil with kinematic viscosity of 50 cSt present the optimal ER efficiency, and the fluids based on the silicone oil with kinematic viscosity of 100 cSt show the shortest response time and good sedimentation stability. The mechanism is that the silicone oil with larger viscosity provides larger viscous force, but makes the nanoparticles easier to agglomerate.
Electrorheological (ER) fluids were fabricated by dispersing oxalate group-modified amorphous titanium oxide nanoparticles in dimethyl silicone oil with different kinematic viscosities (10 cSt, 50 cSt, 100 cSt, 500 cSt and 1000 cSt). The yield stress, zero-field viscosity, ER efficiency, response time, and sedimentation stability were tested to find the influence of the viscosity of silicone oil on the properties of ER fluids. The results indicate that the ER fluids based on the silicone oil with kinematic viscosity of 50 cSt present the optimal ER efficiency, and the fluids based on the silicone oil with kinematic viscosity of 100 cSt show the shortest response time and good sedimentation stability. The mechanism is that the silicone oil with larger viscosity provides larger viscous force, but makes the nanoparticles easier to agglomerate.
2013, 30(5): 55-60.
Abstract:
A novel kind of transparent conductive film was prepared by coating silver nanowires solution on polyethylene terephthalate (PET) surface and then heating pressing under a flat heating pressure. The bending resistant performance, the transmission ratio and surface resistivity of the conductive film were studied. Results show that the transmission ratio and surface resistivity of the silver nanowire-PET transparent conductive films could reach to 80% and 1×10-3 Ω·cm, respectively. Surface conductivity has not changed under 500 cycles bending measurement. The transmission ratio of silver nanowire-PET transparent conductive films decreases with increasing the content of silver nanowires in solution, while the surface resistivity is improved.
A novel kind of transparent conductive film was prepared by coating silver nanowires solution on polyethylene terephthalate (PET) surface and then heating pressing under a flat heating pressure. The bending resistant performance, the transmission ratio and surface resistivity of the conductive film were studied. Results show that the transmission ratio and surface resistivity of the silver nanowire-PET transparent conductive films could reach to 80% and 1×10-3 Ω·cm, respectively. Surface conductivity has not changed under 500 cycles bending measurement. The transmission ratio of silver nanowire-PET transparent conductive films decreases with increasing the content of silver nanowires in solution, while the surface resistivity is improved.
Simulation and verification of cure-induced deformation by stages for integrated composite structure
2013, 30(5): 61-66.
Abstract:
The developing law of T800/epoxy prepreg property parameters during curing process was analyzed through tests. A finite element analysis (FEA) simulation method of staged cure-induced deformation based on stress transfer was proposed in view of phased molding of composite integrated structures under the autoclave conditions. For I-shaped stiffened structures fabricated in different processes, deformation results predicted by the phased simulation were compared to experimental results and relationships between different manufacture schemes and deformations were also analyzed. The results show that the simulation method proposed in this paper can accurately predict the cure-induced deformations for the integrated structures, deformation is closely correlated with fabrication process, and selecting appropriate fabrication process for special structure and lay-up can effectively reduce the cured-induced deformations of composite structures.
The developing law of T800/epoxy prepreg property parameters during curing process was analyzed through tests. A finite element analysis (FEA) simulation method of staged cure-induced deformation based on stress transfer was proposed in view of phased molding of composite integrated structures under the autoclave conditions. For I-shaped stiffened structures fabricated in different processes, deformation results predicted by the phased simulation were compared to experimental results and relationships between different manufacture schemes and deformations were also analyzed. The results show that the simulation method proposed in this paper can accurately predict the cure-induced deformations for the integrated structures, deformation is closely correlated with fabrication process, and selecting appropriate fabrication process for special structure and lay-up can effectively reduce the cured-induced deformations of composite structures.
Compacting pressure measuring method in autoclave processing of polymer composites using film sensor
2013, 30(5): 67-73.
Abstract:
For autoclave processing of polymer composite laminates, a compacting pressure on-line measuring system using film pressure sensor was established to monitor the value and distribution of compacting pressure on composites during processing. The applicability of the compacting pressure measuring system in autoclave processing was studied. The variation of compacting pressure in autoclave processing for L-shaped carbon fiber/epoxy laminates and the effects of mold configurations were investigated using the measuring system. The results show that the measuring system is accurate and is good in dynamic response. It can be used in high temperature and measure the compacting pressure on curved surfaces. These properties meet the requirements of compacting pressure on-line measuring for composites in autoclave processing. The compacting pressures at the corner and in the flat section for L-shaped composite laminates increase with the autoclave pressure during fabrication, but their increasing speeds and the final values are different. The compacting pressure at the corner is larger than that in the flat section during convex tool molding, while the compacting pressure at the corner is less than that in the flat section and the external pressure during concave tool molding. These experimental results demonstrate that the compacting behavior in curved part is different from that in flat structure.
For autoclave processing of polymer composite laminates, a compacting pressure on-line measuring system using film pressure sensor was established to monitor the value and distribution of compacting pressure on composites during processing. The applicability of the compacting pressure measuring system in autoclave processing was studied. The variation of compacting pressure in autoclave processing for L-shaped carbon fiber/epoxy laminates and the effects of mold configurations were investigated using the measuring system. The results show that the measuring system is accurate and is good in dynamic response. It can be used in high temperature and measure the compacting pressure on curved surfaces. These properties meet the requirements of compacting pressure on-line measuring for composites in autoclave processing. The compacting pressures at the corner and in the flat section for L-shaped composite laminates increase with the autoclave pressure during fabrication, but their increasing speeds and the final values are different. The compacting pressure at the corner is larger than that in the flat section during convex tool molding, while the compacting pressure at the corner is less than that in the flat section and the external pressure during concave tool molding. These experimental results demonstrate that the compacting behavior in curved part is different from that in flat structure.
2013, 30(5): 74-78.
Abstract:
Glass fiber fabric (5HS)/epoxy resin E51 prepreg was prepared to study the applicability of on-line resin pressure measuring system during autoclave process in this paper. The effect of viscosity on the dynamic response properties was analyzed. In addition, the resin pressures inside flat, tapered and L-shaped prepreg stacks under zero-bleeding condition were measured by this system and calculated from theoretical model, respectively. These experimental data were additionally compared with theoretical ones to assess its accuracy. The results show that the viscosity greatly influences the dynamic response of the system. As the viscosity of resin is less than 25 Pa·s, the high dynamic response can meet the requirements of resin pressure measurement inside composites. In addition, the measured resin pressures inside prepreg stacks with different shapes involved in this paper are consistent with the theoretical ones. As the autoclave pressure reaches to 0.5 MPa, the relative errors are approximately 2%, and the accuracy of the system is validated.
Glass fiber fabric (5HS)/epoxy resin E51 prepreg was prepared to study the applicability of on-line resin pressure measuring system during autoclave process in this paper. The effect of viscosity on the dynamic response properties was analyzed. In addition, the resin pressures inside flat, tapered and L-shaped prepreg stacks under zero-bleeding condition were measured by this system and calculated from theoretical model, respectively. These experimental data were additionally compared with theoretical ones to assess its accuracy. The results show that the viscosity greatly influences the dynamic response of the system. As the viscosity of resin is less than 25 Pa·s, the high dynamic response can meet the requirements of resin pressure measurement inside composites. In addition, the measured resin pressures inside prepreg stacks with different shapes involved in this paper are consistent with the theoretical ones. As the autoclave pressure reaches to 0.5 MPa, the relative errors are approximately 2%, and the accuracy of the system is validated.
2013, 30(5): 79-85.
Abstract:
Intumescent flame-retardant polypropylene(PP) was reinforced by Kevlar pulp(PPTA-pulp).The composites of PPTA-pulp-intumescent flame retardant(IFR)/PP were prepared by one step blending method. The effects of the PPTA-pulp contents on the mechanical properties, the flame retardant properties and the thermal stability of the composites were studied. The results indicate that the PPTA-pulp-IFR/PP composites show the highest values of mechanical properties, tensile strength 40.0 MPa, impact strength 56.9 J·m-1, limited oxygen index (LOI) 28% and the vertical firing ranks UL-94 V-0, when the mass fraction of PPTA-pulp treated by silicon coupling agent KH-550 reaches 5%.The thermal stability and the residue mass of the composite are improved respectively. The SEM results show good affinity between the PPTA-pulp treated by KH-550 and the PP matrix.
Intumescent flame-retardant polypropylene(PP) was reinforced by Kevlar pulp(PPTA-pulp).The composites of PPTA-pulp-intumescent flame retardant(IFR)/PP were prepared by one step blending method. The effects of the PPTA-pulp contents on the mechanical properties, the flame retardant properties and the thermal stability of the composites were studied. The results indicate that the PPTA-pulp-IFR/PP composites show the highest values of mechanical properties, tensile strength 40.0 MPa, impact strength 56.9 J·m-1, limited oxygen index (LOI) 28% and the vertical firing ranks UL-94 V-0, when the mass fraction of PPTA-pulp treated by silicon coupling agent KH-550 reaches 5%.The thermal stability and the residue mass of the composite are improved respectively. The SEM results show good affinity between the PPTA-pulp treated by KH-550 and the PP matrix.
2013, 30(5): 86-93.
Abstract:
Wheat straw/polypropylene(PP) wood-plastic composites (WPC) filled with 50% wheat straw powder were prepared by mixing compression molding. WPC were accelerated ageing by ultra violet (UV) radiation. The mechanical properties and color change of the original and ageing PP wood-plastic composites filled with different plant fiber were investigated. UV weathering mechanism was analyzed by FTIR. The tensile sections of the composites were observed by SEM. The results show that the mechanical performance decreases substantially caused by the UV accelerated ageing. When the aging time is less than 960 h, bending strength and tensile strength decrease slightly. Then the mechanical performance decreases rapidly and WPC fade obviously. Bending strength, tensile strength and impact strength decrease respectively 67.2%, 47.89%, 32.41% when ageing time is 1200 h. The hydroxyl in the wheat straw fiber evidently accelerates the degradation of PP. Finally the partial fiber drops out from the face of material with cracks while PP occurs pulverization phenomena.
Wheat straw/polypropylene(PP) wood-plastic composites (WPC) filled with 50% wheat straw powder were prepared by mixing compression molding. WPC were accelerated ageing by ultra violet (UV) radiation. The mechanical properties and color change of the original and ageing PP wood-plastic composites filled with different plant fiber were investigated. UV weathering mechanism was analyzed by FTIR. The tensile sections of the composites were observed by SEM. The results show that the mechanical performance decreases substantially caused by the UV accelerated ageing. When the aging time is less than 960 h, bending strength and tensile strength decrease slightly. Then the mechanical performance decreases rapidly and WPC fade obviously. Bending strength, tensile strength and impact strength decrease respectively 67.2%, 47.89%, 32.41% when ageing time is 1200 h. The hydroxyl in the wheat straw fiber evidently accelerates the degradation of PP. Finally the partial fiber drops out from the face of material with cracks while PP occurs pulverization phenomena.
2013, 30(5): 94-100.
Abstract:
Wood flour/polypropylene foamed composites with different content of wood flour were prepared using compression molding.The energy absorption properties of these foamed composites were investigated by the tests of static compression, cycle compression, compression creep and dynamic thermal mechanical analysis. The results show that properties such as energy absorbing capacity, energy absorbing efficiency parameter, the relaxation rate, circulation loss quantity, dynamic mechanical properties of foamed composites all first increase then decrease following with wood flour increasing. When the wood flour mass ratio is 30%, the energy absorption properties of foamed composites are the best.
Wood flour/polypropylene foamed composites with different content of wood flour were prepared using compression molding.The energy absorption properties of these foamed composites were investigated by the tests of static compression, cycle compression, compression creep and dynamic thermal mechanical analysis. The results show that properties such as energy absorbing capacity, energy absorbing efficiency parameter, the relaxation rate, circulation loss quantity, dynamic mechanical properties of foamed composites all first increase then decrease following with wood flour increasing. When the wood flour mass ratio is 30%, the energy absorption properties of foamed composites are the best.
2013, 30(5): 101-106.
Abstract:
The interface of bamboo fibers(BF) reinforced polylactic acid(PLA) composites was regulated by hydroxide and isocyanate, and BF/PLA composites were prepared by injection molding process. The thermal aging properties of BF/PLA composites were studied by the methods of FTIR, XRD, gel permeation chromatography (GPC) and SEM. The results show that the C O in the molecular chains of PLA are continuously hydrolyzed, the C—O in the molecular chains of PLA are fractured and generated the PLA of smaller molecular weight and lower polymerization degree, the crystallinity degree of PLA is reduced, the bonding interface between BF and PLA is destroyed, the tensile strength and impact strength gradually decrease with the increasing of aging time in the thermal aging process. The tensile strength and impact strength of the BF/PLA composites reduce by 75% and 77.6% after thermal aging at 80℃ for 16 days, while the tensile strength and impact strength of the BF/PLA composites reduce by 80.3% and 83.4% after thermal aging at 100℃ for 32 h. The effect made by temperature on the aging property of BF/PLA composites is significant, the higher the temperature, the faster the aging.
The interface of bamboo fibers(BF) reinforced polylactic acid(PLA) composites was regulated by hydroxide and isocyanate, and BF/PLA composites were prepared by injection molding process. The thermal aging properties of BF/PLA composites were studied by the methods of FTIR, XRD, gel permeation chromatography (GPC) and SEM. The results show that the C O in the molecular chains of PLA are continuously hydrolyzed, the C—O in the molecular chains of PLA are fractured and generated the PLA of smaller molecular weight and lower polymerization degree, the crystallinity degree of PLA is reduced, the bonding interface between BF and PLA is destroyed, the tensile strength and impact strength gradually decrease with the increasing of aging time in the thermal aging process. The tensile strength and impact strength of the BF/PLA composites reduce by 75% and 77.6% after thermal aging at 80℃ for 16 days, while the tensile strength and impact strength of the BF/PLA composites reduce by 80.3% and 83.4% after thermal aging at 100℃ for 32 h. The effect made by temperature on the aging property of BF/PLA composites is significant, the higher the temperature, the faster the aging.
2013, 30(5): 107-112.
Abstract:
The waste corrugated paper was grinded to paper pulp, and used to prepare the foamed waste paper pulp/starch composites by injection molding foaming with starch, polyving akohol and foamer of azodicarbonamide-zinc oxide(AC-ZnO). The double-barrel capillary rheometer was used to research the influence of waste paper pulp content, mixed plasticizer of glycerol and dioctyl-phthalate(G-DOP) content, compatilizer of polyacrylic acid (EAA) content, foamer of AC-ZnO content and temperature on the rheological behavior of the composites melt. SEM was also used to observe the effect of different viscosity of melt on the cell morphologies. The results show that: the melt performs of the waste paper pulp/starch foam composites are pseudoplastic flow. The viscosity of melt is significantly reduced with the content of mixed plasticizer increasing, decreased with increasing of AC-ZnO content and increased with the content of the waste paper pulp and EAA increasing. The viscosity of melt is firstly decreased with the temperature rising, then increased. The number of cell increases and size of cell becomes smaller with the viscosity decreasing. When the viscosity is 900 Pa·s, cells happens to rupture and merge.
The waste corrugated paper was grinded to paper pulp, and used to prepare the foamed waste paper pulp/starch composites by injection molding foaming with starch, polyving akohol and foamer of azodicarbonamide-zinc oxide(AC-ZnO). The double-barrel capillary rheometer was used to research the influence of waste paper pulp content, mixed plasticizer of glycerol and dioctyl-phthalate(G-DOP) content, compatilizer of polyacrylic acid (EAA) content, foamer of AC-ZnO content and temperature on the rheological behavior of the composites melt. SEM was also used to observe the effect of different viscosity of melt on the cell morphologies. The results show that: the melt performs of the waste paper pulp/starch foam composites are pseudoplastic flow. The viscosity of melt is significantly reduced with the content of mixed plasticizer increasing, decreased with increasing of AC-ZnO content and increased with the content of the waste paper pulp and EAA increasing. The viscosity of melt is firstly decreased with the temperature rising, then increased. The number of cell increases and size of cell becomes smaller with the viscosity decreasing. When the viscosity is 900 Pa·s, cells happens to rupture and merge.
2013, 30(5): 113-118.
Abstract:
In terms of the geopolymer is a new type of cementitious materials, which has a low carbon emission and a less energy and resource consumption, the preparation technology has attracted much attention.The geopolymer was prepared by the thermal activated sludge and high calcium coal waste, the reaction mechanism and property of this kind of geopolymer were comparative analysed to that of geopolymer which was prepared by high calcium fly ash and gangue, then the optimal technological parameters were determined. Raw material composition and properties of the prepared geopolymer were deeply analysed by XRD, SEM, TG-DTA and FTIR.The results show that the compressive strength of the geopolymer is higher when 40% coal waste is replaced by thermal activated sludge (<50 μm) at 900℃ for 45 min. In complex geopolymeric matrix, amorphous geopolymeric gel covers around the spherical fly ahs granule, similar zeolite mineral forms, and asymmetric stretching Al—O/Si—O bonds and Si—O—Si/Si—O—Al bending band appear obviously.
In terms of the geopolymer is a new type of cementitious materials, which has a low carbon emission and a less energy and resource consumption, the preparation technology has attracted much attention.The geopolymer was prepared by the thermal activated sludge and high calcium coal waste, the reaction mechanism and property of this kind of geopolymer were comparative analysed to that of geopolymer which was prepared by high calcium fly ash and gangue, then the optimal technological parameters were determined. Raw material composition and properties of the prepared geopolymer were deeply analysed by XRD, SEM, TG-DTA and FTIR.The results show that the compressive strength of the geopolymer is higher when 40% coal waste is replaced by thermal activated sludge (<50 μm) at 900℃ for 45 min. In complex geopolymeric matrix, amorphous geopolymeric gel covers around the spherical fly ahs granule, similar zeolite mineral forms, and asymmetric stretching Al—O/Si—O bonds and Si—O—Si/Si—O—Al bending band appear obviously.
2013, 30(5): 119-124.
Abstract:
Cu-0.6%Zr (mass fraction) alloy powders were prepared by using high-pressure water atomization with non-vacuum melting, and ZrO2/Cu in-situ reinforced composite was prepared after particle size separation, following by low-temperature oxidation, N2+5%H2 (volume fraction) mixture reduction and vacuum spark plasma sintering(SPS) forming. The results show that lower temperature leads to lower oxidation rate, while higher temperature leads to over oxidation and agglomeration, and the ideal oxidation parameter is 230℃×1 h; In N2+5%H2 gas flow of 200 mL/min, the best reduction parameter is 250℃×1 h which is measured by hydrogen-annealed experiment; Under the condition of 30 MPa, 850℃×2 h vacuum SPS, the typical performance of the ZrO2/Cu sample has been obtained that the conductivity is higher than 83% IACS(international annealed copper standard), the hardness is higher than HB 75 and the softening temperature is 900℃.
Cu-0.6%Zr (mass fraction) alloy powders were prepared by using high-pressure water atomization with non-vacuum melting, and ZrO2/Cu in-situ reinforced composite was prepared after particle size separation, following by low-temperature oxidation, N2+5%H2 (volume fraction) mixture reduction and vacuum spark plasma sintering(SPS) forming. The results show that lower temperature leads to lower oxidation rate, while higher temperature leads to over oxidation and agglomeration, and the ideal oxidation parameter is 230℃×1 h; In N2+5%H2 gas flow of 200 mL/min, the best reduction parameter is 250℃×1 h which is measured by hydrogen-annealed experiment; Under the condition of 30 MPa, 850℃×2 h vacuum SPS, the typical performance of the ZrO2/Cu sample has been obtained that the conductivity is higher than 83% IACS(international annealed copper standard), the hardness is higher than HB 75 and the softening temperature is 900℃.
2013, 30(5): 125-131.
Abstract:
WCP-NiCrBSi/refractory steel composite was fabricated by vacuum fusion sintering. The composite was constructed with rod-like WCP-NiCrBSi array within refractory steel matrix. This composite material structure could realize well compromise between hardness and toughness. The microstructures of the composite interface and WCP-NiCrBSi reinforcement were characterized using SEM, EDS and microhardness. The elevated temperature wear behavior of the composite was evaluated on ring-on-disc wear tester and compared with the unreinforced refractory steel. The results show that a metallurgical binding free from cracks and pores is produced between the refractory steel matrix and the WCP-NiCrBSi reinforcement. γ-Ni solid solution layer adjacent to the WCP-NiCrBSi reinforcement is formed by isothermal solidification and a large number of fine Fe-Cr-B precipitates are generated in the diffusion affected zone adjacent to the matrix due to mutual diffusion of elements. WCP are evenly dispersed within the WCP-NiCrBSi reinforcement and γ-Ni(Ni3Si), Ni-B, Cr-B and multiple eutectic are formed during the solidification of NiCrBSi alloy. In the temperature range from room temperature to 600℃, the wear resistance of the WCP-NiCrBSi/refractory composite is better than that of the unreinforced refractory steel. The wear resistance advantage of the composite at room temperature is maximum, and gradually decreases as the temperature increases. At room temperature, the wear mechanism of the composite is mild adhesive wear regime due to WCP preventing metal to metal contact. WCP-NiCrBSi/refractory steel the composite exhibits mild oxidation wear at 300℃ and 600℃ owing to the oxide film formation on the worn surface.
WCP-NiCrBSi/refractory steel composite was fabricated by vacuum fusion sintering. The composite was constructed with rod-like WCP-NiCrBSi array within refractory steel matrix. This composite material structure could realize well compromise between hardness and toughness. The microstructures of the composite interface and WCP-NiCrBSi reinforcement were characterized using SEM, EDS and microhardness. The elevated temperature wear behavior of the composite was evaluated on ring-on-disc wear tester and compared with the unreinforced refractory steel. The results show that a metallurgical binding free from cracks and pores is produced between the refractory steel matrix and the WCP-NiCrBSi reinforcement. γ-Ni solid solution layer adjacent to the WCP-NiCrBSi reinforcement is formed by isothermal solidification and a large number of fine Fe-Cr-B precipitates are generated in the diffusion affected zone adjacent to the matrix due to mutual diffusion of elements. WCP are evenly dispersed within the WCP-NiCrBSi reinforcement and γ-Ni(Ni3Si), Ni-B, Cr-B and multiple eutectic are formed during the solidification of NiCrBSi alloy. In the temperature range from room temperature to 600℃, the wear resistance of the WCP-NiCrBSi/refractory composite is better than that of the unreinforced refractory steel. The wear resistance advantage of the composite at room temperature is maximum, and gradually decreases as the temperature increases. At room temperature, the wear mechanism of the composite is mild adhesive wear regime due to WCP preventing metal to metal contact. WCP-NiCrBSi/refractory steel the composite exhibits mild oxidation wear at 300℃ and 600℃ owing to the oxide film formation on the worn surface.
Influence of the BiFeO3 phase on ferromagnet properties of layered multiferroic CoFe2O4-BiFeO3 films
2013, 30(5): 132-137.
Abstract:
Multiferroic layered films consisting of CoFe2O4-BiFeO3(CFO-BFO) with increasing BFO constituent layers thicknesses were prepared on the LaNiO3(LNO)-buffered Si(100) substrate via a simple spin-coating process in order to investigate the thickness effect of ferroelectric BiFeO3 phase on the magnetic properties of the composite films. The structure and morphology were researched by XRD, SEM and TEM. Bisides, the magnetic properties were demonstrated by vibrating sample magnetometer (VSM) and the effect of different thicknesses of BFO layer on the magnetic properties of the composite films was discussed. The results reveal that magnetic CFO and ferroelectric BFO phases coexist in the heterostructured films. The buffered layer LNO and ferromagnetic layer CFO possess clear microstructure and obvious interface between them. The thickness of BiFeO3 phase has a significant influence on the magnetic properties of the CFO-BFO films. Among the multiferroic films containing different BFO layers, the film that consisting of nine BFO constituent layers demonstrates the highest Ms value of 230 emu·cm-3, which improves 18.6% than that of the film without BFO constituent layers. We initially conclude that it is stress that leads to the improvement of Ms with increasing the BFO thickness.
Multiferroic layered films consisting of CoFe2O4-BiFeO3(CFO-BFO) with increasing BFO constituent layers thicknesses were prepared on the LaNiO3(LNO)-buffered Si(100) substrate via a simple spin-coating process in order to investigate the thickness effect of ferroelectric BiFeO3 phase on the magnetic properties of the composite films. The structure and morphology were researched by XRD, SEM and TEM. Bisides, the magnetic properties were demonstrated by vibrating sample magnetometer (VSM) and the effect of different thicknesses of BFO layer on the magnetic properties of the composite films was discussed. The results reveal that magnetic CFO and ferroelectric BFO phases coexist in the heterostructured films. The buffered layer LNO and ferromagnetic layer CFO possess clear microstructure and obvious interface between them. The thickness of BiFeO3 phase has a significant influence on the magnetic properties of the CFO-BFO films. Among the multiferroic films containing different BFO layers, the film that consisting of nine BFO constituent layers demonstrates the highest Ms value of 230 emu·cm-3, which improves 18.6% than that of the film without BFO constituent layers. We initially conclude that it is stress that leads to the improvement of Ms with increasing the BFO thickness.
2013, 30(5): 138-143.
Abstract:
Gd2Zr2O7 was prepared by solid state synthesis and its phase stability and thermo-physical properties were investigated. The Gd2Zr2O7-8YSZ(8%Y2O3-ZrO2) double-ceramic-layer thermal barrier coatings was prepared by electron beam physical vapour deposition. The crystal structure and atomic number ratio of the top coating were analysed. Results reveal that Gd2Zr2O7 powders show excellent phase stability up to 1500℃, 250℃ higher as compared to the conventional 8YSZ.The coefficients of thermal expansion of the Gd2Zr2O7 bulk ranges from 8.8×10-6-11.0×10-6 K-1 at the temperature from 100 to 1500℃, which are comparable to that of the 8YSZ bulk.The thermal conductivities of the Gd2Zr2O7 bulk are in a level of 1.0 W(m·K)-1 at 1000-1400℃ and about 50% lower than that of the conventional 8YSZ. The as-deposited Gd2Zr2O7 coating with pyrochlore structure has a stoichiometrical composition and exhibits a typical columnar grain structure.
Gd2Zr2O7 was prepared by solid state synthesis and its phase stability and thermo-physical properties were investigated. The Gd2Zr2O7-8YSZ(8%Y2O3-ZrO2) double-ceramic-layer thermal barrier coatings was prepared by electron beam physical vapour deposition. The crystal structure and atomic number ratio of the top coating were analysed. Results reveal that Gd2Zr2O7 powders show excellent phase stability up to 1500℃, 250℃ higher as compared to the conventional 8YSZ.The coefficients of thermal expansion of the Gd2Zr2O7 bulk ranges from 8.8×10-6-11.0×10-6 K-1 at the temperature from 100 to 1500℃, which are comparable to that of the 8YSZ bulk.The thermal conductivities of the Gd2Zr2O7 bulk are in a level of 1.0 W(m·K)-1 at 1000-1400℃ and about 50% lower than that of the conventional 8YSZ. The as-deposited Gd2Zr2O7 coating with pyrochlore structure has a stoichiometrical composition and exhibits a typical columnar grain structure.
2013, 30(5): 144-150.
Abstract:
A novel silicon-zirconium (Si-Zr) composite adsorbent was prepared via co-precipitation approach. The surface morphology and chemical structure of the prepared Si-Zr composites were characterized by SEM, FTIR and XRD. The influence of synthesis conditions on the performance of defluorination was observed and evaluated. The results show that with 600℃ of calcination temperature, the Si-Zr composites exhibits blooming porous structure and large specific surface, which benefits the absorption of aqueous fluoride. Zirconium and silicon in the material are combined as Si—O—Zr composite oxides. Additionally, the prepared composites can bond stably with fluoride anion and are resistive in desorption. The comprehensive experiments reveal that calcination temperature and time, ratio of raw material (ZrOCl2∶Na2SiO3) dominate the application performance of the Si-Zr composites.
A novel silicon-zirconium (Si-Zr) composite adsorbent was prepared via co-precipitation approach. The surface morphology and chemical structure of the prepared Si-Zr composites were characterized by SEM, FTIR and XRD. The influence of synthesis conditions on the performance of defluorination was observed and evaluated. The results show that with 600℃ of calcination temperature, the Si-Zr composites exhibits blooming porous structure and large specific surface, which benefits the absorption of aqueous fluoride. Zirconium and silicon in the material are combined as Si—O—Zr composite oxides. Additionally, the prepared composites can bond stably with fluoride anion and are resistive in desorption. The comprehensive experiments reveal that calcination temperature and time, ratio of raw material (ZrOCl2∶Na2SiO3) dominate the application performance of the Si-Zr composites.
2013, 30(5): 151-158.
Abstract:
In order to reveal the moisture absorption mechanism of ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced epoxy composites, the two-dimensional finite element models were established by using ABAQUS, and the hygroscopic behavior and moisture-induced stress in the composites were studied. The moisture concentration fields in two models with different fiber distributions and environment temperatures were calculated, and then the moisture-induced stresses were analyzed on the basis of the first step. The results show that the moisture absorption processes of the two models all are in agreement with Fick’s diffusion law, the saturation time of moisture absorption of the model with hexagonally distributed fibers is less than that of the model with randomly distributed fibers, but the latter is more coincidental with practical situation and fitted well with the experimental data. The stress within the materials induced by long time moisture absorption can reach to a higher level (above 60 MPa), the higher the temperature, the more early the moisture absorption balance, the greater the stress, and the maximal value appears in the matrix region where fiber aggregation state is most crowded. The stress level of the model with randomly distributed fibers is obviously higher than that of the model with hexagonally distributed fibers.
In order to reveal the moisture absorption mechanism of ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced epoxy composites, the two-dimensional finite element models were established by using ABAQUS, and the hygroscopic behavior and moisture-induced stress in the composites were studied. The moisture concentration fields in two models with different fiber distributions and environment temperatures were calculated, and then the moisture-induced stresses were analyzed on the basis of the first step. The results show that the moisture absorption processes of the two models all are in agreement with Fick’s diffusion law, the saturation time of moisture absorption of the model with hexagonally distributed fibers is less than that of the model with randomly distributed fibers, but the latter is more coincidental with practical situation and fitted well with the experimental data. The stress within the materials induced by long time moisture absorption can reach to a higher level (above 60 MPa), the higher the temperature, the more early the moisture absorption balance, the greater the stress, and the maximal value appears in the matrix region where fiber aggregation state is most crowded. The stress level of the model with randomly distributed fibers is obviously higher than that of the model with hexagonally distributed fibers.
2013, 30(5): 159-165.
Abstract:
A new interfacial element composed of a zero thickness cohesive element and eight rigid elements was introduced. Such interfacial elements were placed at the interface of shell structures to model the initiation and growth of delamination along the interface. The translational and rotational nodal movements of the adjacent shell element contributed to the deformation of the cohesive element. The type of the interfacial element was of finite thickness and eight-nodes, each of them possessed five degrees of freedom for coping with the corresponding shell element node. The rigid elements transfered nodal displacements and forces of the shell elements to the zero-thickness cohesive element by which the interlaminar damages were exhibited. The mixed mode bending (MMB) and double cantilever beam (DCB) bending tests were simulated by the shell and proposed elements, and the results agree pretty well with the experiments. Comparing with the traditional model of solid elements connected by cohesive elements, shell elements coupled with the suggested interfacial elements are easier to be used for the sheet-like or laminated structures with internal interfaces. The latter allows larger element size in the cohesive zone, reducing the total model scale and enhancing the computational efficiency.
A new interfacial element composed of a zero thickness cohesive element and eight rigid elements was introduced. Such interfacial elements were placed at the interface of shell structures to model the initiation and growth of delamination along the interface. The translational and rotational nodal movements of the adjacent shell element contributed to the deformation of the cohesive element. The type of the interfacial element was of finite thickness and eight-nodes, each of them possessed five degrees of freedom for coping with the corresponding shell element node. The rigid elements transfered nodal displacements and forces of the shell elements to the zero-thickness cohesive element by which the interlaminar damages were exhibited. The mixed mode bending (MMB) and double cantilever beam (DCB) bending tests were simulated by the shell and proposed elements, and the results agree pretty well with the experiments. Comparing with the traditional model of solid elements connected by cohesive elements, shell elements coupled with the suggested interfacial elements are easier to be used for the sheet-like or laminated structures with internal interfaces. The latter allows larger element size in the cohesive zone, reducing the total model scale and enhancing the computational efficiency.
2013, 30(5): 166-173.
Abstract:
Based on the meso-structure of three-dimensional and six-directional braided composites and assuming that the cross-section of weft yarn on the sixth direction was diamond, a representative volume element (RVE)-based micromechanical damage model was presented to predict the damage propagation and strength of three-dimensional and six-directional braided composites. The stress-strain relation of three-dimensional and six-directional braided composites was simulated by using failure criteria proposed by Linde and the periodicity boundary condition. The progressive damage of three-dimensional and six-directional braided composites was studied subjected to longitudinal tensile loading, and ultimate strength of the sample was obtained. Furthermore, the changing characteristics of mechanical properties with the material parameters of braided composites were discussed. The results show that the main factor to break the three-dimensional and six-directional braided composites is longitudinal tensile breakage of axial yarns, and the FEM results are in a good agreement with experimental data, which confirms the effectiveness of the model and provides a basis for the analysis of mechanical properties.
Based on the meso-structure of three-dimensional and six-directional braided composites and assuming that the cross-section of weft yarn on the sixth direction was diamond, a representative volume element (RVE)-based micromechanical damage model was presented to predict the damage propagation and strength of three-dimensional and six-directional braided composites. The stress-strain relation of three-dimensional and six-directional braided composites was simulated by using failure criteria proposed by Linde and the periodicity boundary condition. The progressive damage of three-dimensional and six-directional braided composites was studied subjected to longitudinal tensile loading, and ultimate strength of the sample was obtained. Furthermore, the changing characteristics of mechanical properties with the material parameters of braided composites were discussed. The results show that the main factor to break the three-dimensional and six-directional braided composites is longitudinal tensile breakage of axial yarns, and the FEM results are in a good agreement with experimental data, which confirms the effectiveness of the model and provides a basis for the analysis of mechanical properties.
2013, 30(5): 174-179.
Abstract:
The post-buckling loading capability of the box was analyzed with the commercial software ABAQUS, focusing on the failure of skin/flange interface induced by post-buckling under bend-twist loading. Based on the FEM results, the skin/flange interface was enhanced by stitch which was simulated by using cohesive element, and the impact of stitch on failure mode and loading capability of the box was discussed. Moreover, the loading capability of reinforced box was studied by testing. The FEM results show that the multi-spar composite box has a long post-buckling period, and the post-buckling loading capability of the box reinforced by stitching technique could be improved significantly. The predicted results coincide well with experimental data, and the failure mode is also consistent with test results.
The post-buckling loading capability of the box was analyzed with the commercial software ABAQUS, focusing on the failure of skin/flange interface induced by post-buckling under bend-twist loading. Based on the FEM results, the skin/flange interface was enhanced by stitch which was simulated by using cohesive element, and the impact of stitch on failure mode and loading capability of the box was discussed. Moreover, the loading capability of reinforced box was studied by testing. The FEM results show that the multi-spar composite box has a long post-buckling period, and the post-buckling loading capability of the box reinforced by stitching technique could be improved significantly. The predicted results coincide well with experimental data, and the failure mode is also consistent with test results.
2013, 30(5): 180-186.
Abstract:
A numerical study on fluid flow characteristics and heat transfer performance of composite lattice truss core sandwich structure with a constant localized internal heat source was presented. The thermal resistance network and the non-dimensional parameters measured by the channel height were respectively adopted to analysis and characterize the thermal field of heat source and active cooling performance. The effects of inclination angle on fluid flow and temperature of heat source were explored. An optimization analysis of thermo-mechanical performance was carried out based on the relationship between inclination angle and the maximum temperature of heat source. The results suggest that this composite sandwich structure has excellent active cooling performance, and with an increase of inclination angle, the heat transfer efficiency is improved, leading to a reduction of structural maximum temperature.
A numerical study on fluid flow characteristics and heat transfer performance of composite lattice truss core sandwich structure with a constant localized internal heat source was presented. The thermal resistance network and the non-dimensional parameters measured by the channel height were respectively adopted to analysis and characterize the thermal field of heat source and active cooling performance. The effects of inclination angle on fluid flow and temperature of heat source were explored. An optimization analysis of thermo-mechanical performance was carried out based on the relationship between inclination angle and the maximum temperature of heat source. The results suggest that this composite sandwich structure has excellent active cooling performance, and with an increase of inclination angle, the heat transfer efficiency is improved, leading to a reduction of structural maximum temperature.
2013, 30(5): 187-194.
Abstract:
The flexural behavior of the repaired honeycomb sandwich structures, which were made up of carbon fiber reinforced polymer (CFRP) skins and honeycomb material, was investigated by four-point bending test. The bending performance of the repaired plate was analyzed under the influence of scarf ratio, flush repair method, damage size, repair equipment and repair material.The test results show that, the failure modes of all the repaired plate can be divided into three kinds: breaking at the edge of the patch, breaking at the middle of the patch and breaking at the adhesive film surface. The failure strength of the specimens with the same failure mode is close. The bending strength of the repaired plate of which the first two failure modes plate is similar to the undamaged plate, while the bending strength of the repaired plate of the third failure mode is relatively low. The strength recovery of all the repaired plate is basically higher than 95%. The analysis on the relative stiffness of sandwich structures shows that the stiffness of the repaired structures is close to the undamaged plate, which is consistent with the composite repair criterion.
The flexural behavior of the repaired honeycomb sandwich structures, which were made up of carbon fiber reinforced polymer (CFRP) skins and honeycomb material, was investigated by four-point bending test. The bending performance of the repaired plate was analyzed under the influence of scarf ratio, flush repair method, damage size, repair equipment and repair material.The test results show that, the failure modes of all the repaired plate can be divided into three kinds: breaking at the edge of the patch, breaking at the middle of the patch and breaking at the adhesive film surface. The failure strength of the specimens with the same failure mode is close. The bending strength of the repaired plate of which the first two failure modes plate is similar to the undamaged plate, while the bending strength of the repaired plate of the third failure mode is relatively low. The strength recovery of all the repaired plate is basically higher than 95%. The analysis on the relative stiffness of sandwich structures shows that the stiffness of the repaired structures is close to the undamaged plate, which is consistent with the composite repair criterion.
2013, 30(5): 195-200.
Abstract:
This paper demonstrated design studies of aeroelastic optimization on composite skins of a high-aspect-ratio wing, subject to aeroelastic constraints and strength/strain constraints. In optimization, the ply thickness of wing skin panels was adopted as design variables. The impacts of laminate proportion and unbalance laminate of wing skin panels on optimization results meeting all design constraints were discussed. The results indicate that the maximal vertical deformation and twist angle at wing tip and the flutter speed decrease with the proportion of 0°plies increasing, and there is less variation in the aileron efficiencies of the optimal results. The optimal distribution has made it clear that the unbalance level of the skin laminates has great effects on the static aeroelastic characteristics. The maximal twist angle at wing tip increases with the axis of stiffness moving forward, while the maximal vertical deformation at wing tip keeps almost unchanged, but the aileron efficiency decreases.
This paper demonstrated design studies of aeroelastic optimization on composite skins of a high-aspect-ratio wing, subject to aeroelastic constraints and strength/strain constraints. In optimization, the ply thickness of wing skin panels was adopted as design variables. The impacts of laminate proportion and unbalance laminate of wing skin panels on optimization results meeting all design constraints were discussed. The results indicate that the maximal vertical deformation and twist angle at wing tip and the flutter speed decrease with the proportion of 0°plies increasing, and there is less variation in the aileron efficiencies of the optimal results. The optimal distribution has made it clear that the unbalance level of the skin laminates has great effects on the static aeroelastic characteristics. The maximal twist angle at wing tip increases with the axis of stiffness moving forward, while the maximal vertical deformation at wing tip keeps almost unchanged, but the aileron efficiency decreases.
2013, 30(5): 201-208.
Abstract:
In order to investigate the in-plane shear behaviour of S2-glass/epoxy composite laminate, continum damage mechanics (CDM) model involving elasticity and plasticity for S2-glass/epoxy laminate under in-plane shear loading was studied in this paper. Typical in-plane tensile shear tests of the composite were conducted, two types of CDM models were established based on the plane stress assumption and the parameters were identified. The former CDM model considered no plasticity while the later one did. Both two CDM models were coded to VUMAT through ABAQUS/Explicit, finite element analysis (FEA) for in-plane shear behaviour of the composite was conducted by them following experimental tests. The results of FEA were compared with experiments and the influence of plasticity on the in-plane shear behaviour of the composite was discussed. Element types on the results of FEA were also analyzed. The results show that the CDM model considering no plasticity can exactly predict the failure strength of S2-glass/epoxy composite under in-plane shear loading, but it can not well predict the nonlinear mechanical behaviour. However, when coupled with isotropic plasticity criteria, the CDM model can perfectly predict the nonlinear mechanical behavior, and the result of failure strength is also acceptable compared with the experimental results. The CDM models can also be used for FEA simulation by shell elements, but the results of load-deflection curve are a little lower than that using plane stress elements because of the transverse shear behaviour of shell elements. Moreover, reduced integration method is found to be beneficial for FEA simulation.
In order to investigate the in-plane shear behaviour of S2-glass/epoxy composite laminate, continum damage mechanics (CDM) model involving elasticity and plasticity for S2-glass/epoxy laminate under in-plane shear loading was studied in this paper. Typical in-plane tensile shear tests of the composite were conducted, two types of CDM models were established based on the plane stress assumption and the parameters were identified. The former CDM model considered no plasticity while the later one did. Both two CDM models were coded to VUMAT through ABAQUS/Explicit, finite element analysis (FEA) for in-plane shear behaviour of the composite was conducted by them following experimental tests. The results of FEA were compared with experiments and the influence of plasticity on the in-plane shear behaviour of the composite was discussed. Element types on the results of FEA were also analyzed. The results show that the CDM model considering no plasticity can exactly predict the failure strength of S2-glass/epoxy composite under in-plane shear loading, but it can not well predict the nonlinear mechanical behaviour. However, when coupled with isotropic plasticity criteria, the CDM model can perfectly predict the nonlinear mechanical behavior, and the result of failure strength is also acceptable compared with the experimental results. The CDM models can also be used for FEA simulation by shell elements, but the results of load-deflection curve are a little lower than that using plane stress elements because of the transverse shear behaviour of shell elements. Moreover, reduced integration method is found to be beneficial for FEA simulation.
2013, 30(5): 209-217.
Abstract:
A mathematical model for resin flow was established, the geometry model close to the real unit cell structure was built based on the principle of minimum potential energy. The influence of yarn crimp and extrusion on micro-permeability was studied and the numerical method for solving the resin flow control equations based on finite difference method was built, the pressure and velocity distribution of the flow were computed to predict the permeability of preform. The prediction results were compared with literature and experimental values to verify the prediction model and the solving method mentioned above.
A mathematical model for resin flow was established, the geometry model close to the real unit cell structure was built based on the principle of minimum potential energy. The influence of yarn crimp and extrusion on micro-permeability was studied and the numerical method for solving the resin flow control equations based on finite difference method was built, the pressure and velocity distribution of the flow were computed to predict the permeability of preform. The prediction results were compared with literature and experimental values to verify the prediction model and the solving method mentioned above.
2013, 30(5): 218-225.
Abstract:
The external low-velocity impact identification problem was investigated on a cylindrical stiffened composite structure. The piezoelectric sensors were used to obtain the stress wave signals when the structure was impacted by a foreign object with low-velocity. Aiming at the problem that the impact location identification of a stiffened composite structure and especially the location identification when the impact occurring near edges of the monitoring region, a two-step positioning method based on the power of sensor signals was proposed to estimate the impact location. The impact force was reconstructed by the system-identification method, furthermore, the relationship between the model order of the transfer function and the correlation coefficients was analyzed and the principle of the model order selection was suggested to supplement this method. The results indicate that the proposed positioning method can estimate impact locations with high precision regardless the impact occurring region, and the improved system-identification method can identify the location and force time history effectively when an impact event doesn’t occur in the region with stiffener; however, when an impact occurring on the region with stiffener, the impact can not be well identified due to the complex influence of stiffeners on stress wave propagation.
The external low-velocity impact identification problem was investigated on a cylindrical stiffened composite structure. The piezoelectric sensors were used to obtain the stress wave signals when the structure was impacted by a foreign object with low-velocity. Aiming at the problem that the impact location identification of a stiffened composite structure and especially the location identification when the impact occurring near edges of the monitoring region, a two-step positioning method based on the power of sensor signals was proposed to estimate the impact location. The impact force was reconstructed by the system-identification method, furthermore, the relationship between the model order of the transfer function and the correlation coefficients was analyzed and the principle of the model order selection was suggested to supplement this method. The results indicate that the proposed positioning method can estimate impact locations with high precision regardless the impact occurring region, and the improved system-identification method can identify the location and force time history effectively when an impact event doesn’t occur in the region with stiffener; however, when an impact occurring on the region with stiffener, the impact can not be well identified due to the complex influence of stiffeners on stress wave propagation.
2013, 30(5): 226-235.
Abstract:
According to different mechanical states and energy-dissipative mechanisms during penetration process, together with the high-velocity penetration-resistant characteristic of ultra-high molecular weight polyethylene fiber reinforced plastics (UFRP), the whole process of high-velocity blunt-nosed projectiles penetrating moderately thick UFRP is divided into three consecutive phases, i.e., compression & mushrooming phase, shearing & compression phase and stretching deformation phase. Based on three-phase penetration mechanism, an analytical model was developed to compute ballistic limits and residual velocities of projectiles penetrating moderately thick UFRP. Ballistic limits and residual velocities of projectiles for different test cases in a correlative reference were calculated by the model. Good agreements are obtained between the calculated values and experimental results. The three-phase penetration model, which considers the phenomenons of melted fibers due to frictions and mushrooming of projectiles existing in ballistic tests, can be employed to reasonably predict ballistic limits and residual velocities of high-velocity blunt-nosed projectiles penetrating moderately thick UFRP. The model has theoretical and engineering application values.
According to different mechanical states and energy-dissipative mechanisms during penetration process, together with the high-velocity penetration-resistant characteristic of ultra-high molecular weight polyethylene fiber reinforced plastics (UFRP), the whole process of high-velocity blunt-nosed projectiles penetrating moderately thick UFRP is divided into three consecutive phases, i.e., compression & mushrooming phase, shearing & compression phase and stretching deformation phase. Based on three-phase penetration mechanism, an analytical model was developed to compute ballistic limits and residual velocities of projectiles penetrating moderately thick UFRP. Ballistic limits and residual velocities of projectiles for different test cases in a correlative reference were calculated by the model. Good agreements are obtained between the calculated values and experimental results. The three-phase penetration model, which considers the phenomenons of melted fibers due to frictions and mushrooming of projectiles existing in ballistic tests, can be employed to reasonably predict ballistic limits and residual velocities of high-velocity blunt-nosed projectiles penetrating moderately thick UFRP. The model has theoretical and engineering application values.
2013, 30(5): 236-243.
Abstract:
A new type of cohesive zone model(CZM) was used to study the composite interlaminar damage in this article. The model consisted of the bilinear damage criterion and damage evolvement could accurately predict the delamination propagation. The resin rich zones were recognized after impregnating referred to as knitting yarn induced fiber distortions (KYD) in the axial reinforced warp-knitted fabric. A new method to study the stress distributing around the KYD region when the unit cell was extruding and shearing was descripted based on the micromechanics theory of composite materials. The distortion is recognized to be dominant for the crack damage initiation. Bending and interlaminar shearing mechanical properties of T700 unidirectional warp-knitted fabric composite were tested. The discrepancy of the maximum strength between simulation and experiment about the bending and shearing is under 10%. The damage in laminates and interlaminar crack propagation damage were studied based on the finite element model.
A new type of cohesive zone model(CZM) was used to study the composite interlaminar damage in this article. The model consisted of the bilinear damage criterion and damage evolvement could accurately predict the delamination propagation. The resin rich zones were recognized after impregnating referred to as knitting yarn induced fiber distortions (KYD) in the axial reinforced warp-knitted fabric. A new method to study the stress distributing around the KYD region when the unit cell was extruding and shearing was descripted based on the micromechanics theory of composite materials. The distortion is recognized to be dominant for the crack damage initiation. Bending and interlaminar shearing mechanical properties of T700 unidirectional warp-knitted fabric composite were tested. The discrepancy of the maximum strength between simulation and experiment about the bending and shearing is under 10%. The damage in laminates and interlaminar crack propagation damage were studied based on the finite element model.
2013, 30(5): 244-250.
Abstract:
The transverse magnetoelectric voltage coefficient of piezoelectric-magnetostrictive bilayer at the electromechanical resonance (EMR) was derived according to the constitutive equations of piezoelectric and magnetostrictive phases, and the equation of motion. As a function of frequency, the transverse magnetoelectric voltage coefficients of Tb1-x Dyx Fe2-y (TDF)-Pb(Zr,Ti) O3 (PZT) bilayer had been calculated using the corresponding material parameters of individual phases. The resonance frequency was calculated using different length and volume fraction of piezoelectric phase, and the dependence of frequency on the two parameters was analyzed. The results indicate that the bilayer shows strong resonance character at resonance frequency. The transverse magnetoelectric voltage coefficient can reach peak value 11.2 V·cm-1·Oe-1 at 55.2 kHz when effective mechanical quality factor is 50, which is about 40 times as high as that at the low frequency (281.9 mV·cm-1·Oe-1). The resonance frequency rises with shortening the length and increasing the volume fraction of piezoelectric phase. TDF-PZT bilayer is fabricated and the relevant experiment is carried out to verify the calculated results. The actual effective mechanical quality factor is about 48.
The transverse magnetoelectric voltage coefficient of piezoelectric-magnetostrictive bilayer at the electromechanical resonance (EMR) was derived according to the constitutive equations of piezoelectric and magnetostrictive phases, and the equation of motion. As a function of frequency, the transverse magnetoelectric voltage coefficients of Tb1-x Dyx Fe2-y (TDF)-Pb(Zr,Ti) O3 (PZT) bilayer had been calculated using the corresponding material parameters of individual phases. The resonance frequency was calculated using different length and volume fraction of piezoelectric phase, and the dependence of frequency on the two parameters was analyzed. The results indicate that the bilayer shows strong resonance character at resonance frequency. The transverse magnetoelectric voltage coefficient can reach peak value 11.2 V·cm-1·Oe-1 at 55.2 kHz when effective mechanical quality factor is 50, which is about 40 times as high as that at the low frequency (281.9 mV·cm-1·Oe-1). The resonance frequency rises with shortening the length and increasing the volume fraction of piezoelectric phase. TDF-PZT bilayer is fabricated and the relevant experiment is carried out to verify the calculated results. The actual effective mechanical quality factor is about 48.
2013, 30(5): 251-257.
Abstract:
Based on the flexural experimental research of five reinforced concrete beams strengthened with near surface mounted carbon fibre reinforced plastics(CFRP)-prestressed concrete prisms (CFRP-PCPs composite reinforcement) of different control tension stress, the characteristics of mean crack width and maximum crack width were acquired with comparison and analysis of crack distribution and development under static loading. The results indicate that this type of the unique composite reinforcement has an inhibitory effect on development of crack width and crack height. Based on the calculation method for crack width in the current national standard and experimental data, the suggested maximum crack width of the reinforced concrete beams strengthened with near surface mounted CFRP-PCPs reinforcement under static loading was given. And the calculated values are revealed to be in reasonable matching the tested value.
Based on the flexural experimental research of five reinforced concrete beams strengthened with near surface mounted carbon fibre reinforced plastics(CFRP)-prestressed concrete prisms (CFRP-PCPs composite reinforcement) of different control tension stress, the characteristics of mean crack width and maximum crack width were acquired with comparison and analysis of crack distribution and development under static loading. The results indicate that this type of the unique composite reinforcement has an inhibitory effect on development of crack width and crack height. Based on the calculation method for crack width in the current national standard and experimental data, the suggested maximum crack width of the reinforced concrete beams strengthened with near surface mounted CFRP-PCPs reinforcement under static loading was given. And the calculated values are revealed to be in reasonable matching the tested value.
