2012 Vol. 29, No. 1
2012, 29(1): 1-7.
Abstract:
A series of nanofillers/liquid crystalline epoxy composites with different nano-fillers were prepared. The curing reaction and phase behavior of 2,5-bis benzoic acid hexanol ester (EP-6)-4,4'-diaminodiphenyl methane (DDM) system were studied by non-isothermal DSC, POM and XRD. The thermal property of the nano-fillers/EP-6-DDM composites was characterized by TGA. It was found that in all the four nano-fillers catalyzed the curing of EP-6-DDM system. SiO2 has the highest catalytic reactivity and organoclay cloisite 30B has the lowest. The XRD data indicated that only exfoliated nanocomposites formed when the mass fraction of 30B is below 1%, while both exfoliated and intercalated nanocomposites formed when the content of 30B is above 3%. Polarizing optical microscope observation showed that the nano-fillers did not change the nematic structure of resin matrix, but retarded the appearance of nematic texture. Thermogravimetric analysis indicated that the thermal stability of cured nano-fillers/EP-6-DDM decreased slightly.
A series of nanofillers/liquid crystalline epoxy composites with different nano-fillers were prepared. The curing reaction and phase behavior of 2,5-bis benzoic acid hexanol ester (EP-6)-4,4'-diaminodiphenyl methane (DDM) system were studied by non-isothermal DSC, POM and XRD. The thermal property of the nano-fillers/EP-6-DDM composites was characterized by TGA. It was found that in all the four nano-fillers catalyzed the curing of EP-6-DDM system. SiO2 has the highest catalytic reactivity and organoclay cloisite 30B has the lowest. The XRD data indicated that only exfoliated nanocomposites formed when the mass fraction of 30B is below 1%, while both exfoliated and intercalated nanocomposites formed when the content of 30B is above 3%. Polarizing optical microscope observation showed that the nano-fillers did not change the nematic structure of resin matrix, but retarded the appearance of nematic texture. Thermogravimetric analysis indicated that the thermal stability of cured nano-fillers/EP-6-DDM decreased slightly.
2012, 29(1): 8-15.
Abstract:
Graphite nanosheets (nano-Gs) were prepared via sonication and then activated with mixed acid, finally the nano-Gs/PVC composites were prepared by way of melt blending. The structure of nano-Gs was characterized by FTIR and SEM, and the impact of nano-Gs on the conductive and mechanical properties of nano-Gs/PVC composites was also studied. The FTIR spectra demonstrate that the surface-active functional groups of nano-Gs increase significantly after mixed acid treatment, which form a certain degree of hydrogen bonding with PVC molecular chains. The SEM micrographs show that nano-Gs have a thickness ranging 30-80 nm and a diameter ranging 4-20 μm, and disperse randomly in PVC resin matrix. The electrical performance testing indicates that with the increase of the filled nano-Gs, the volume resistivity of the nano-Gs/PVC composites decreases nonlinearly and reachs the lowest value of 103Ω·cm when the mass fraction of nano-Gs reachs its percolation threshold (10%). The mechanics performance testing shows that with the increase of the filled nano-Gs, both the tensile strength and notched impact strength of the composites increase first and then decrease, when the mass fraction of nano-Gs is 1%, the tensile strength and notched impact strength achieve the maximal value simultaneously and increase by 14% and 38% respectively compared with the pure PVC.
Graphite nanosheets (nano-Gs) were prepared via sonication and then activated with mixed acid, finally the nano-Gs/PVC composites were prepared by way of melt blending. The structure of nano-Gs was characterized by FTIR and SEM, and the impact of nano-Gs on the conductive and mechanical properties of nano-Gs/PVC composites was also studied. The FTIR spectra demonstrate that the surface-active functional groups of nano-Gs increase significantly after mixed acid treatment, which form a certain degree of hydrogen bonding with PVC molecular chains. The SEM micrographs show that nano-Gs have a thickness ranging 30-80 nm and a diameter ranging 4-20 μm, and disperse randomly in PVC resin matrix. The electrical performance testing indicates that with the increase of the filled nano-Gs, the volume resistivity of the nano-Gs/PVC composites decreases nonlinearly and reachs the lowest value of 103Ω·cm when the mass fraction of nano-Gs reachs its percolation threshold (10%). The mechanics performance testing shows that with the increase of the filled nano-Gs, both the tensile strength and notched impact strength of the composites increase first and then decrease, when the mass fraction of nano-Gs is 1%, the tensile strength and notched impact strength achieve the maximal value simultaneously and increase by 14% and 38% respectively compared with the pure PVC.
Sensitive coefficient of pressure-sensitive sensor based on conductive rubber filled by carbon black
2012, 29(1): 16-20.
Abstract:
An equation of sensitive coefficient of the pressure-sensitive sensor based on conductive rubber filled by carbon black is given by general effective media theory. Sensitive coefficient and working principle of the pressure-sensitive carbon black/rubber are studied by impact of the strain and piezoresistive effect on negative pressure coefficient of resistance (NPC effect). When the volume fraction of carbon black is close to the critical volume fraction, the scope of sensitive coefficient is from 2.5 to 13 and the piezoresistive effect would be the main working principle. When the volume fraction of carbon black is within the percolation zone, the scope of sensitive coefficient is from 2.5 to 4.5 and the mainly working principle is related to the size of contact pressure. When the pressure is relatively low, the piezoresistive effect would play a main role in the work of sensor; and when the pressure is relatively high, the strain effect would play a main role. When the volume fraction of carbon black is within the conductive zone, the scope of sensitive coefficient is from 2.0 to 2.5 and the strain effect would be the main working principle.
An equation of sensitive coefficient of the pressure-sensitive sensor based on conductive rubber filled by carbon black is given by general effective media theory. Sensitive coefficient and working principle of the pressure-sensitive carbon black/rubber are studied by impact of the strain and piezoresistive effect on negative pressure coefficient of resistance (NPC effect). When the volume fraction of carbon black is close to the critical volume fraction, the scope of sensitive coefficient is from 2.5 to 13 and the piezoresistive effect would be the main working principle. When the volume fraction of carbon black is within the percolation zone, the scope of sensitive coefficient is from 2.5 to 4.5 and the mainly working principle is related to the size of contact pressure. When the pressure is relatively low, the piezoresistive effect would play a main role in the work of sensor; and when the pressure is relatively high, the strain effect would play a main role. When the volume fraction of carbon black is within the conductive zone, the scope of sensitive coefficient is from 2.0 to 2.5 and the strain effect would be the main working principle.
2012, 29(1): 21-27.
Abstract:
Several typical functional groups, —OH, —NH2, —COOH and —CH3 were selected in this work. In order to study the effect of the functional groups on calcium carbonate mineralization, the groups were grafted on single crystal silicon chips. The modified chips were used as substrates in the in vitro mineralization experiments. The contact angle was measured to examine the grafting efficiency, and the results showed that the groups were all successfully grafted. Raman was used to determine the crystal form. SEM was used to observe the morphology, size, quantity and orientation of calcium carbonate crystals. The results show that on -OH modified substrate, calcite aggregates are found, on —NH2 and —COOH modified substrates, some vaterites are found with different morphologies, on —CH3 modified substrate, less crystals are found compared with the blank. It is supposed that —OH and —CH3 have no significant control effect over the polymorph of calcium carbonate crystals, —NH2 and —COOH can induce vaterite crystal growth by absorbing CO32- or Ca2+.
Several typical functional groups, —OH, —NH2, —COOH and —CH3 were selected in this work. In order to study the effect of the functional groups on calcium carbonate mineralization, the groups were grafted on single crystal silicon chips. The modified chips were used as substrates in the in vitro mineralization experiments. The contact angle was measured to examine the grafting efficiency, and the results showed that the groups were all successfully grafted. Raman was used to determine the crystal form. SEM was used to observe the morphology, size, quantity and orientation of calcium carbonate crystals. The results show that on -OH modified substrate, calcite aggregates are found, on —NH2 and —COOH modified substrates, some vaterites are found with different morphologies, on —CH3 modified substrate, less crystals are found compared with the blank. It is supposed that —OH and —CH3 have no significant control effect over the polymorph of calcium carbonate crystals, —NH2 and —COOH can induce vaterite crystal growth by absorbing CO32- or Ca2+.
2012, 29(1): 28-34.
Abstract:
The uniaxial time-dependent cyclic of carbon fiber/polyether ether ketone(PEEK) composite was studied experimentally. The volume fraction of carbon fiber was 30%. The property under stress-control led and stress-controlled loading and the ratcheting behaviors of carbon fiber/PEEK composite were discussed under different conditions. It was shown that the creep behavior of carbon fiber/PEEK composite is better than that of PEEK. In the experiment of strain-controlled cyclic, the stress amplitude has a close relationship with the applied strain loading rate and strain amplitude. Due to the stress relaxation, the responded stress amplitude will decreases as the hold time at strain peak increase. The ratcheting occurs in the composite to asymmetrical stress-controlled, and the ratcheting strain depends on the stress amplitude and stress loading rate. The stress holding time and low loading rate lead to an increased ratcheting strain. The carbon fiber will fail as the peak holding time beyond the range.
The uniaxial time-dependent cyclic of carbon fiber/polyether ether ketone(PEEK) composite was studied experimentally. The volume fraction of carbon fiber was 30%. The property under stress-control led and stress-controlled loading and the ratcheting behaviors of carbon fiber/PEEK composite were discussed under different conditions. It was shown that the creep behavior of carbon fiber/PEEK composite is better than that of PEEK. In the experiment of strain-controlled cyclic, the stress amplitude has a close relationship with the applied strain loading rate and strain amplitude. Due to the stress relaxation, the responded stress amplitude will decreases as the hold time at strain peak increase. The ratcheting occurs in the composite to asymmetrical stress-controlled, and the ratcheting strain depends on the stress amplitude and stress loading rate. The stress holding time and low loading rate lead to an increased ratcheting strain. The carbon fiber will fail as the peak holding time beyond the range.
2012, 29(1): 35-42.
Abstract:
Ni plating graphite nanosheet (Ni-nanoG) was prepared by electroless plating method. The technology of preparation of Ni-nanoG and the microstructures of Ni-nanoG were studied to obtain a novel magnetic conductive filler. The influence of Ni sulfuric acid concentration, sodium hypophosphite concentration, temperature, pH value on the deposition quality of Ni on graphite nanosheet (nanoG) and the optimum technology were researched. The microstructures of the as-obtained samples were characterized by SEM, XRD and EDS. The magnetic property of Ni-nanoG was studied via the vibrating samplemagnetometer (VSM). The results indicate that a layer of compact Ni coate on the surface of nanoG and the Ni is homogeneously dispersed on the surface and boundary of nanoG. The thickness of Ni-nanoG is about 150 nm. The content of Ni in Ni-nanoG is high and the amount of Ni is about 34.08%. The saturated magnetic strength of Ni-nanoG is 71.2 A·m2·kg-1. The Ni-nanoG can be used as a new functional filler.
Ni plating graphite nanosheet (Ni-nanoG) was prepared by electroless plating method. The technology of preparation of Ni-nanoG and the microstructures of Ni-nanoG were studied to obtain a novel magnetic conductive filler. The influence of Ni sulfuric acid concentration, sodium hypophosphite concentration, temperature, pH value on the deposition quality of Ni on graphite nanosheet (nanoG) and the optimum technology were researched. The microstructures of the as-obtained samples were characterized by SEM, XRD and EDS. The magnetic property of Ni-nanoG was studied via the vibrating samplemagnetometer (VSM). The results indicate that a layer of compact Ni coate on the surface of nanoG and the Ni is homogeneously dispersed on the surface and boundary of nanoG. The thickness of Ni-nanoG is about 150 nm. The content of Ni in Ni-nanoG is high and the amount of Ni is about 34.08%. The saturated magnetic strength of Ni-nanoG is 71.2 A·m2·kg-1. The Ni-nanoG can be used as a new functional filler.
2012, 29(1): 43-48.
Abstract:
γ-ray total irradiation inducing grafting was used to modify the carbon fiber surface to improve interfacial adhesion properties of the carbon fiber/epoxy composite.The change of surface chemical elements and functional groups composition, surface morphology, fracture surface and interlaminar shear strength(ILSS) of the carbon fiber/epoxy composite after 200 kGy doses of γ-ray radiation in different grafting solutions were studied severally with XPS,SEM,and electronic universal testing machine. The results show that condensed ethylene glycol graft solutions have ideal grafting effect, the carbon fiber grafting rate is 7%. the surface O/C ratio and the content of oxygen functional groups is increased. the ILSS of irradiated carbon fiber/epoxy composite also is increased, the maximum ILSS is increased by the rate of 31.2%. The surface roughness of carbon fiber is increased after irradiation.
γ-ray total irradiation inducing grafting was used to modify the carbon fiber surface to improve interfacial adhesion properties of the carbon fiber/epoxy composite.The change of surface chemical elements and functional groups composition, surface morphology, fracture surface and interlaminar shear strength(ILSS) of the carbon fiber/epoxy composite after 200 kGy doses of γ-ray radiation in different grafting solutions were studied severally with XPS,SEM,and electronic universal testing machine. The results show that condensed ethylene glycol graft solutions have ideal grafting effect, the carbon fiber grafting rate is 7%. the surface O/C ratio and the content of oxygen functional groups is increased. the ILSS of irradiated carbon fiber/epoxy composite also is increased, the maximum ILSS is increased by the rate of 31.2%. The surface roughness of carbon fiber is increased after irradiation.
2012, 29(1): 49-53.
Abstract:
Carbon/carbon(C/C)composites are often used in heat-resistant layers of aircrafts with a high Mach number as they can withstand a high temperature, yet which may be ablated due to high pressure and heat flow. According to Fourier heat transfer law and high temperature ablation mechanism, we utilized FORTRAN programming to calculate and analyze the performance of thermal conduction in C/C plates with ablation, considering the thermal conductivity of C/C composites as a function of temperature at high temperature. The results show: when lower heat flow acts, compared with that the thermal conductivity is constant, the temperature change rate of object surface is different from that of interior; over time, the surface temperature is gradually consistent, but the back temperature is distinct extremely; the distribution trend of object interior temperature is basically same. When higher heat flow acts, the ablation phenomenon occurs on the surface, at the same time, the temperature rapidly increases, which will maintain dynamic equilibrium.
Carbon/carbon(C/C)composites are often used in heat-resistant layers of aircrafts with a high Mach number as they can withstand a high temperature, yet which may be ablated due to high pressure and heat flow. According to Fourier heat transfer law and high temperature ablation mechanism, we utilized FORTRAN programming to calculate and analyze the performance of thermal conduction in C/C plates with ablation, considering the thermal conductivity of C/C composites as a function of temperature at high temperature. The results show: when lower heat flow acts, compared with that the thermal conductivity is constant, the temperature change rate of object surface is different from that of interior; over time, the surface temperature is gradually consistent, but the back temperature is distinct extremely; the distribution trend of object interior temperature is basically same. When higher heat flow acts, the ablation phenomenon occurs on the surface, at the same time, the temperature rapidly increases, which will maintain dynamic equilibrium.
2012, 29(1): 54-61.
Abstract:
A colloidal shear thickening fluid(STF) was generated by dispersing self-made SiO2 particles with different size in 200 molecular weight polyethylene glycol(PEG200) using the ball-milling technique. The STF/Kevlar composites were prepared by the static impregnation method. The effect of particle size on the rheological behavior of the fluid systems and the stab resistant properties of STF/Kevlar composites were studied. The results show that the suspensions with different SiO2 particle sizes all have notable shear thickening behavior. Under the condition of the same SiO2 mass fraction, the initial viscosity, critical shear rate and highest viscosity of fluid system decrease as the particle size increasing. 16-layer STF/Kevlar targets provide protection without penetration against spike at the impacted energy of 24.0 J, which are significantly better than that of the pure Kevlar with equal areal density. As the particle size increases, the composite targets have better stab resistance against spike. Under the impacted energy of 13.0 J, the STF/Kevlar targets exhibit better stab resistance against knife than that of the pure Kevlar target with equal areal density. As the particle size increases, the depth of penetration into the backing material decreases. Shear fracture is the main damage form of the targets.
A colloidal shear thickening fluid(STF) was generated by dispersing self-made SiO2 particles with different size in 200 molecular weight polyethylene glycol(PEG200) using the ball-milling technique. The STF/Kevlar composites were prepared by the static impregnation method. The effect of particle size on the rheological behavior of the fluid systems and the stab resistant properties of STF/Kevlar composites were studied. The results show that the suspensions with different SiO2 particle sizes all have notable shear thickening behavior. Under the condition of the same SiO2 mass fraction, the initial viscosity, critical shear rate and highest viscosity of fluid system decrease as the particle size increasing. 16-layer STF/Kevlar targets provide protection without penetration against spike at the impacted energy of 24.0 J, which are significantly better than that of the pure Kevlar with equal areal density. As the particle size increases, the composite targets have better stab resistance against spike. Under the impacted energy of 13.0 J, the STF/Kevlar targets exhibit better stab resistance against knife than that of the pure Kevlar target with equal areal density. As the particle size increases, the depth of penetration into the backing material decreases. Shear fracture is the main damage form of the targets.
2012, 29(1): 62-68.
Abstract:
High density pine fiberboard (HDF) with good fire performance was successfully prepared by using flame retardants of industrial by-product(mainly composed of aluminum trihydrate Al(OH)3), zinc borate (2ZnO·3B2O3·3.5H2O) and boric acid (H3BO3). The mechanical properties, flame retardancy and char morphology were characterized and analyzed. The results show that there is a good synergistic effect on the flame-retardancy between Al(OH)3 and 2ZnO·3B2O3·3.5H2O and H3BO3 which can enhance the char formation up to 22.2% and reduce the total heat release with a dop of 32%, while the mechanical properties are well maintained. The limited oxygen index (LOI) of the flame retardancy board can reach up to 36.4% and the vertical burning test can reach V-0.
High density pine fiberboard (HDF) with good fire performance was successfully prepared by using flame retardants of industrial by-product(mainly composed of aluminum trihydrate Al(OH)3), zinc borate (2ZnO·3B2O3·3.5H2O) and boric acid (H3BO3). The mechanical properties, flame retardancy and char morphology were characterized and analyzed. The results show that there is a good synergistic effect on the flame-retardancy between Al(OH)3 and 2ZnO·3B2O3·3.5H2O and H3BO3 which can enhance the char formation up to 22.2% and reduce the total heat release with a dop of 32%, while the mechanical properties are well maintained. The limited oxygen index (LOI) of the flame retardancy board can reach up to 36.4% and the vertical burning test can reach V-0.
2012, 29(1): 69-72.
Abstract:
Al-flake/poly(vinylidene)fluoride(PVDF) composite was prepared by ball-milling process with ethanol, which used PVDF and Al as matrix and filler, respectively. The dielectric properties of the Al-flake/PVDF composites with different volume fractions of Al were studied, the surface morphologies of the samples were examined by SEM and the elements of the samples were analysed by EDS. The results show that the addition of Al-flake not only can increase the dielectric constant, but also has a low loss tangent and high breakdown field strength, which demonstrate that Al-flake/PVDF composites can be used in the electronic industry.
Al-flake/poly(vinylidene)fluoride(PVDF) composite was prepared by ball-milling process with ethanol, which used PVDF and Al as matrix and filler, respectively. The dielectric properties of the Al-flake/PVDF composites with different volume fractions of Al were studied, the surface morphologies of the samples were examined by SEM and the elements of the samples were analysed by EDS. The results show that the addition of Al-flake not only can increase the dielectric constant, but also has a low loss tangent and high breakdown field strength, which demonstrate that Al-flake/PVDF composites can be used in the electronic industry.
2012, 29(1): 73-78.
Abstract:
An intumescent flame retardant 3, 9-dichloro-2, 4, 8, 10-tetraoxa-3, 9-diphosphaspiro-[5.5] undecane-3, 9-dioxide (SPDPC)-hexamethylendiamine copolymer (PSPHD) molecules containing active end-group were grafted onto the sepiolite (SEP) surface via condensation between acryl chloride of PSPHD and hydroxyl groups existed on sepiolite surface successfully. The modified sepiolite were characterized by SEM, TEM, XPS, FTIR, XRD, TGA. SEP/LDPE and PSPHD-SEP/LDPE composites were prepared by melt blending. SEM and TEM photographs illustrate that the surface morphology of sepiolite changes rapidly. The results of XPS, FTIR and XRD show a grafting modification effect on the structure of SEP, but no destruction. The results of TGA and DTG confirm that there really exists a grafting reaction between PSPHD and SEP, the thermal degradation process of SEP change through graftion. The limiting oxygen index (LOI) test results indicate that the flame retardancy of LDPE can be improved with the addition of PSPHD-SEP or SEP, the LOI value of PSPHD-SEP /LDPE composite reaches 23 with 5% mass fraction of PSPHD-SEP.
An intumescent flame retardant 3, 9-dichloro-2, 4, 8, 10-tetraoxa-3, 9-diphosphaspiro-[5.5] undecane-3, 9-dioxide (SPDPC)-hexamethylendiamine copolymer (PSPHD) molecules containing active end-group were grafted onto the sepiolite (SEP) surface via condensation between acryl chloride of PSPHD and hydroxyl groups existed on sepiolite surface successfully. The modified sepiolite were characterized by SEM, TEM, XPS, FTIR, XRD, TGA. SEP/LDPE and PSPHD-SEP/LDPE composites were prepared by melt blending. SEM and TEM photographs illustrate that the surface morphology of sepiolite changes rapidly. The results of XPS, FTIR and XRD show a grafting modification effect on the structure of SEP, but no destruction. The results of TGA and DTG confirm that there really exists a grafting reaction between PSPHD and SEP, the thermal degradation process of SEP change through graftion. The limiting oxygen index (LOI) test results indicate that the flame retardancy of LDPE can be improved with the addition of PSPHD-SEP or SEP, the LOI value of PSPHD-SEP /LDPE composite reaches 23 with 5% mass fraction of PSPHD-SEP.
2012, 29(1): 79-84.
Abstract:
ZrO2/Al2O3 green bodies were prepared using a low-toxicity monomer N, N-dimethyl acrylamide (DMAA). The effects of the amount of dispersant, ZrO2/Al2O3 suspensions pH value, ZrO2 content in ZrO2/Al2O3 powders, solid volume fraction of ZrO2/Al2O3 powders in slurries, ball-milled time and DMAA content (mass fraction) in the premix solution on the viscosity of ZrO2/Al2O3 slurries were discussed. The mechanical properties and microstructure of ZrO2/Al2O3 green body by gelcasting were investigated.The results show that low viscosity ZrO2/Al2O3 suspension was obtained when the suspension pH is 9, the dispersant content is 0.6% of ZrO2/Al2O3 powders (mass ratio), the ball-milled time is 6 h. The viscosity of suspensions increases with increasing solid volume fraction and DMAA content, but decrease with increasing the content of ZrO2. The resultant green body has uniform structure and the bending strength is as high as 25 MPa.
ZrO2/Al2O3 green bodies were prepared using a low-toxicity monomer N, N-dimethyl acrylamide (DMAA). The effects of the amount of dispersant, ZrO2/Al2O3 suspensions pH value, ZrO2 content in ZrO2/Al2O3 powders, solid volume fraction of ZrO2/Al2O3 powders in slurries, ball-milled time and DMAA content (mass fraction) in the premix solution on the viscosity of ZrO2/Al2O3 slurries were discussed. The mechanical properties and microstructure of ZrO2/Al2O3 green body by gelcasting were investigated.The results show that low viscosity ZrO2/Al2O3 suspension was obtained when the suspension pH is 9, the dispersant content is 0.6% of ZrO2/Al2O3 powders (mass ratio), the ball-milled time is 6 h. The viscosity of suspensions increases with increasing solid volume fraction and DMAA content, but decrease with increasing the content of ZrO2. The resultant green body has uniform structure and the bending strength is as high as 25 MPa.
2012, 29(1): 85-90.
Abstract:
Stearic acid/SiO2 form-stable phase change material (PCM) was synthesized by sol-gel process under ultrasound assisted. Stearic acid acted as latent heat storage material, tetraethyl orthosilicate (TEOS) acted as silica precursor. In order to research the preparation process of the form-stable PCM, the sol-gel processes assisted by different ultrasound power and different kinds of catalyst were analyzed. At last, the maximum stearic acid loading mass fraction of hybrid PCMs with good form-stable character was found to be 60%. The formation process of stearic acid/SiO2 PCM has many advantages such as the whole process without any solvent or surfactant, fast gel formation and convenient preparation. The structure and thermal performance of stearic acid/SiO2 form-stable PCM were analyzed by FTIR, DSC and TG. The results show that the latent heat of stearic acid/SiO2 form-stable PCM is 91.46 J/g, and this material has a good thermal stability below 175℃.
Stearic acid/SiO2 form-stable phase change material (PCM) was synthesized by sol-gel process under ultrasound assisted. Stearic acid acted as latent heat storage material, tetraethyl orthosilicate (TEOS) acted as silica precursor. In order to research the preparation process of the form-stable PCM, the sol-gel processes assisted by different ultrasound power and different kinds of catalyst were analyzed. At last, the maximum stearic acid loading mass fraction of hybrid PCMs with good form-stable character was found to be 60%. The formation process of stearic acid/SiO2 PCM has many advantages such as the whole process without any solvent or surfactant, fast gel formation and convenient preparation. The structure and thermal performance of stearic acid/SiO2 form-stable PCM were analyzed by FTIR, DSC and TG. The results show that the latent heat of stearic acid/SiO2 form-stable PCM is 91.46 J/g, and this material has a good thermal stability below 175℃.
High temperature anti-oxidation mechanism of residual Si in SiC coating prepared by pack cementation
2012, 29(1): 91-97.
Abstract:
The SiC coating for C/C composite was prepared by pack cementation technique.The phase composition and microstructure of SiC coating was analysed by XRD and SEM.The oxidation behavior of the composites with SiC coating was investigated at 1500℃ in air. The results show that coatings are mainly composed of α-SiC, β-SiC and free Si, and the XRD semi-quantitative analysis shows the content of free Si is different. The coating is more integrity with the higher content of free Si. The oxidation test shows that appropriate amount of free Si of coating can protect C/C composites better. As the residual Si's mass fraction is about 1.3% or 2.9%, the anti-oxidation performance of coating are good. The mass-loss of these SiC coated sample is respectively 0.19% and 0.16% after oxidation at 1500℃ in air for 7 h.
The SiC coating for C/C composite was prepared by pack cementation technique.The phase composition and microstructure of SiC coating was analysed by XRD and SEM.The oxidation behavior of the composites with SiC coating was investigated at 1500℃ in air. The results show that coatings are mainly composed of α-SiC, β-SiC and free Si, and the XRD semi-quantitative analysis shows the content of free Si is different. The coating is more integrity with the higher content of free Si. The oxidation test shows that appropriate amount of free Si of coating can protect C/C composites better. As the residual Si's mass fraction is about 1.3% or 2.9%, the anti-oxidation performance of coating are good. The mass-loss of these SiC coated sample is respectively 0.19% and 0.16% after oxidation at 1500℃ in air for 7 h.
2012, 29(1): 98-103.
Abstract:
C-SiC-TaC-C multi-interlayers were introduced in the carbon fiber/carbon matrix interface in quasi 3D needled carbon felt by chemical vapor infiltration, the modified C/C porous performs were densified by impregnation-carbonization processes to obtain C/C composites with C-SiC-TaC-C multi-interlayers. The microstructure and mechanical properties were studied after heat treatment (HTT) at different temperatures of 1400～2500℃. The results show that the SiC-TaC interlayers have a tubular structure before HTT; while the average flexural strength of the as-prepared composites is 241.6 MPa with a brittle fracture. After HTT at 1400～1800℃, TaC interlayer is damaged to granular structure; As a result, the flexural strength of the composites declines to 238.9～226.1 MPa also with a brittle fracture, but an increasing of fracture displacement from 0.7 mm to 1.0 mm. After HTT at 2000～2500℃, both SiC and TaC interlayer are damaged. The flexural strength sharply declines to 158.7～131.8 MPa with an obvious change of fracture behavior from brittleness to pseudo-ductility.
C-SiC-TaC-C multi-interlayers were introduced in the carbon fiber/carbon matrix interface in quasi 3D needled carbon felt by chemical vapor infiltration, the modified C/C porous performs were densified by impregnation-carbonization processes to obtain C/C composites with C-SiC-TaC-C multi-interlayers. The microstructure and mechanical properties were studied after heat treatment (HTT) at different temperatures of 1400～2500℃. The results show that the SiC-TaC interlayers have a tubular structure before HTT; while the average flexural strength of the as-prepared composites is 241.6 MPa with a brittle fracture. After HTT at 1400～1800℃, TaC interlayer is damaged to granular structure; As a result, the flexural strength of the composites declines to 238.9～226.1 MPa also with a brittle fracture, but an increasing of fracture displacement from 0.7 mm to 1.0 mm. After HTT at 2000～2500℃, both SiC and TaC interlayer are damaged. The flexural strength sharply declines to 158.7～131.8 MPa with an obvious change of fracture behavior from brittleness to pseudo-ductility.
2012, 29(1): 104-110.
Abstract:
In the paper, the high toughness matrix Ti3SiC2 was in-situ formed by the joint process of slurry infiltration and liquid silicon infiltration, and Ti3SiC2 modified C/C-SiC composites were obtained. The effect of introduction of TiC particle on the infiltration of molten silicon were studied, and the microstructure and mechanical properties of C/C-SiC-Ti3SiC2 composites were analysed. The results show Ti3SiC2 can be formed by the reaction of TiC with liquid silicon during liquid silicon infiltration, and the existence of carbon is beneficial to the formation of Ti3SiC2. The infiltration depth of molten silicon in the micropore (mean size 22.3 μm) can reach to 10.8 cm in one minute. The in-situ formed Ti3SiC2 replaces the residue silicon and improves both the flexural strength and the fracture toughness of C/C-SiC-Ti3SiC2 composites, which reach to 203 MPa and 8.8 MPa·m1/2, respectively. For C/C-SiC-Ti3SiC2 composites with the depth of 20 mm, the materials with different infiltration depths displays similar phase composition, density and mechanical properties, and no obvious microstructure gradient exist, which indicate the joint process of slurry infiltration and liquid silicon infiltration can be used to fabricate the thick-wall components.
In the paper, the high toughness matrix Ti3SiC2 was in-situ formed by the joint process of slurry infiltration and liquid silicon infiltration, and Ti3SiC2 modified C/C-SiC composites were obtained. The effect of introduction of TiC particle on the infiltration of molten silicon were studied, and the microstructure and mechanical properties of C/C-SiC-Ti3SiC2 composites were analysed. The results show Ti3SiC2 can be formed by the reaction of TiC with liquid silicon during liquid silicon infiltration, and the existence of carbon is beneficial to the formation of Ti3SiC2. The infiltration depth of molten silicon in the micropore (mean size 22.3 μm) can reach to 10.8 cm in one minute. The in-situ formed Ti3SiC2 replaces the residue silicon and improves both the flexural strength and the fracture toughness of C/C-SiC-Ti3SiC2 composites, which reach to 203 MPa and 8.8 MPa·m1/2, respectively. For C/C-SiC-Ti3SiC2 composites with the depth of 20 mm, the materials with different infiltration depths displays similar phase composition, density and mechanical properties, and no obvious microstructure gradient exist, which indicate the joint process of slurry infiltration and liquid silicon infiltration can be used to fabricate the thick-wall components.
2012, 29(1): 111-116.
Abstract:
The nanoscale magnetic composite powders SrFe12O19-NiFe2O4 with core-shell structure were prepared by two-step citrate sol-gel, with Fe(NO3)3Ni(NO3)2 and Sr(NO3)2 as the main materials. The XRD, TEM, VSM and vector network analyzer were used to analyze the structure, feature and absorbing quality of the nano-powder. The results show that the phase structure of the powder is related to the content of NiFe2O4, when the mass ratio of SrFe12O19 to NiFe2O4 is 1∶2 and calcined temperature is 1050℃, the phase of the powder is similar than that of NiFe2O4, the magnetization(Ms)of SrFe12O19 and the coreshell nano-powde raises from 42.6 emu/g to 51.4 emu/g, and the coercivity(Hc) is 336 Oe, which is between that of SrFe12O19 (5395 Oe) and NiFe2O4 (160 Oe). The absorbing quality is enhanced when the frequency is from 8 GHz to 18 GHz. When the frequency is 12 GHz, the microwave absorption can reach maximum point which is -9.7 dB. The composite nano-powder is an excellent absorbing material.
The nanoscale magnetic composite powders SrFe12O19-NiFe2O4 with core-shell structure were prepared by two-step citrate sol-gel, with Fe(NO3)3Ni(NO3)2 and Sr(NO3)2 as the main materials. The XRD, TEM, VSM and vector network analyzer were used to analyze the structure, feature and absorbing quality of the nano-powder. The results show that the phase structure of the powder is related to the content of NiFe2O4, when the mass ratio of SrFe12O19 to NiFe2O4 is 1∶2 and calcined temperature is 1050℃, the phase of the powder is similar than that of NiFe2O4, the magnetization(Ms)of SrFe12O19 and the coreshell nano-powde raises from 42.6 emu/g to 51.4 emu/g, and the coercivity(Hc) is 336 Oe, which is between that of SrFe12O19 (5395 Oe) and NiFe2O4 (160 Oe). The absorbing quality is enhanced when the frequency is from 8 GHz to 18 GHz. When the frequency is 12 GHz, the microwave absorption can reach maximum point which is -9.7 dB. The composite nano-powder is an excellent absorbing material.
2012, 29(1): 117-121.
Abstract:
A series of Ti-doped LaNiO3 photocatalysts were successfully prepared by solution combustion synthesis (SCS). The influence of Ti contents on the phase, morphology and photocatalytic properties were investigated. The synthesized powders were characterized by XRD、 SEM、 EDS and PL. The results show that Ti-doped LaNiO3 with a single perovskite structure can be synthesized by SCS, and the crystal interplanar spacing increases with the increased Ti contents. All the obtained particles have a regular spherical shape with the average size of about 80 nm. The MO(methyl orange)degradation shows that the sample with 3% mass fraction of Ti content has the best photocatalytic efficiency. A proper Ti content can largely decrease the recombination of charge carriers.
A series of Ti-doped LaNiO3 photocatalysts were successfully prepared by solution combustion synthesis (SCS). The influence of Ti contents on the phase, morphology and photocatalytic properties were investigated. The synthesized powders were characterized by XRD、 SEM、 EDS and PL. The results show that Ti-doped LaNiO3 with a single perovskite structure can be synthesized by SCS, and the crystal interplanar spacing increases with the increased Ti contents. All the obtained particles have a regular spherical shape with the average size of about 80 nm. The MO(methyl orange)degradation shows that the sample with 3% mass fraction of Ti content has the best photocatalytic efficiency. A proper Ti content can largely decrease the recombination of charge carriers.
2012, 29(1): 122-128.
Abstract:
[Ni(CH3COO)2+PVP]-[Zn(CH3COO)2+PVP]-[Ti(OC4H9)4+CH3COOH+PVP] composite cables had been fabricated through modified electrospinning equipment. NiO-ZnTiO3-TiO2 coaxial trilayered nanocables were obtained by the calcination of the relevant composite cables at 600℃. The samples were characterized by use of thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Formation mechanism of NiO-ZnTiO3-TiO2 coaxial trilayered nanocables was preliminarily proposed. The results show that the samples are NiO-ZnTiO3-TiO2 coaxial trilayered nanocables. The core layer is NiO, and its diameter is about (42.024±4.405) nm. The middle layer is ZnTiO3, and its thickness is about (55.385±7.681) nm. The outer layer is TiO2, the thickness is about (70.747±7.373) nm.
[Ni(CH3COO)2+PVP]-[Zn(CH3COO)2+PVP]-[Ti(OC4H9)4+CH3COOH+PVP] composite cables had been fabricated through modified electrospinning equipment. NiO-ZnTiO3-TiO2 coaxial trilayered nanocables were obtained by the calcination of the relevant composite cables at 600℃. The samples were characterized by use of thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Formation mechanism of NiO-ZnTiO3-TiO2 coaxial trilayered nanocables was preliminarily proposed. The results show that the samples are NiO-ZnTiO3-TiO2 coaxial trilayered nanocables. The core layer is NiO, and its diameter is about (42.024±4.405) nm. The middle layer is ZnTiO3, and its thickness is about (55.385±7.681) nm. The outer layer is TiO2, the thickness is about (70.747±7.373) nm.
2012, 29(1): 129-135.
Abstract:
The interfacial crack kinking paths in glass fiber reinforced composite sandwich beams were experimentally investigated with double cantilever beam (DCB) specimens, and a series of polymethacrylimid (PMI) foam core with different densities was considered. According to the specimens numerical models were built by material point method(MPM). Mode mixity and kinking angle were calculated with different facing-to-core modulus ratio, and crack kinking paths were simulated. A good accordance was found between numerical results and experimental observations which demonstrates that the MPM algorithm and numerical model presented in this paper is efficiency and accuracy. The result indicates that if kinking occurs bigger kinking angle will be obtained with stronger facing-to-core modulus mismatch, and after kinking into the core the crack will propagate parallel to the face/core interface because the loading becomes highly mode Ⅰ dominated.
The interfacial crack kinking paths in glass fiber reinforced composite sandwich beams were experimentally investigated with double cantilever beam (DCB) specimens, and a series of polymethacrylimid (PMI) foam core with different densities was considered. According to the specimens numerical models were built by material point method(MPM). Mode mixity and kinking angle were calculated with different facing-to-core modulus ratio, and crack kinking paths were simulated. A good accordance was found between numerical results and experimental observations which demonstrates that the MPM algorithm and numerical model presented in this paper is efficiency and accuracy. The result indicates that if kinking occurs bigger kinking angle will be obtained with stronger facing-to-core modulus mismatch, and after kinking into the core the crack will propagate parallel to the face/core interface because the loading becomes highly mode Ⅰ dominated.
2012, 29(1): 136-143.
Abstract:
By proposing a new conformal mapping and using the Stroh formula, the fracture problem of a power function curved crack in an infinite piezoelectric composite is studied under anti-plane shear stress and in-plane electric load at infinity. The analytical solutions of the field intensity factors and the mechanical strain energy release rate are presented with the assumption that the surface of the crack is electrically impermeable. When the power of the curve is zero, the present results can be reduced to the solutions of a Griffith crack in an infinite piezoelectric composite. Based on the analytical solutions, it is found that the distribution of electric field is independent on the mechanics load under a fixed shape of the curve. Numerical examples are finally conducted to analyze the influences of the projected length along the x1-axis, power and coefficient of curved cracks on the mechanical strain energy release rate. The results show that if the piezoelectric composite is subjected to the only load along the direction of x2-axis, there exists a critical projected length along the x1-axis which can promote the crack growth easily for given power and coefficient of curved cracks. Moreover, for given values of projected length and power of curved cracks, the smaller coefficient of curved crack is, the easier crack propagates.
By proposing a new conformal mapping and using the Stroh formula, the fracture problem of a power function curved crack in an infinite piezoelectric composite is studied under anti-plane shear stress and in-plane electric load at infinity. The analytical solutions of the field intensity factors and the mechanical strain energy release rate are presented with the assumption that the surface of the crack is electrically impermeable. When the power of the curve is zero, the present results can be reduced to the solutions of a Griffith crack in an infinite piezoelectric composite. Based on the analytical solutions, it is found that the distribution of electric field is independent on the mechanics load under a fixed shape of the curve. Numerical examples are finally conducted to analyze the influences of the projected length along the x1-axis, power and coefficient of curved cracks on the mechanical strain energy release rate. The results show that if the piezoelectric composite is subjected to the only load along the direction of x2-axis, there exists a critical projected length along the x1-axis which can promote the crack growth easily for given power and coefficient of curved cracks. Moreover, for given values of projected length and power of curved cracks, the smaller coefficient of curved crack is, the easier crack propagates.
2012, 29(1): 144-149.
Abstract:
A method was developed to predict numerically the dent depth of composite laminates subjected to quasi-static indentation. A progressive damage analysis was conducted for composite laminates under quasi-static transverse compressive loading by using a strain based Hashin and Yeh failure criteria as well as the FEM, and a series of degraded elastic constants of the damaged zone were drawn from the numerical results. The effective elastic constants of the damaged zone of the laminates were evaluated according to Sun's explicit expression. Finally, the dent depth vs. indentation force curve was predicted based on Turner's contact theory. The numerical results indicate that the dent initiation is induced by the matrix cracking and delamination, and the transition to rapid increase in dent depth is due to the fiber breakages. The numerical results agree well with the test data for the delamination onset load, the maximum contact force and the corresponding dent depth.
A method was developed to predict numerically the dent depth of composite laminates subjected to quasi-static indentation. A progressive damage analysis was conducted for composite laminates under quasi-static transverse compressive loading by using a strain based Hashin and Yeh failure criteria as well as the FEM, and a series of degraded elastic constants of the damaged zone were drawn from the numerical results. The effective elastic constants of the damaged zone of the laminates were evaluated according to Sun's explicit expression. Finally, the dent depth vs. indentation force curve was predicted based on Turner's contact theory. The numerical results indicate that the dent initiation is induced by the matrix cracking and delamination, and the transition to rapid increase in dent depth is due to the fiber breakages. The numerical results agree well with the test data for the delamination onset load, the maximum contact force and the corresponding dent depth.
2012, 29(1): 150-161.
Abstract:
A 3D rate-dependent constitutive model was developed to simulate damage of laminated polymer matrix composites under high velocity impact. The cohesive elements were involved between two layers to simulate delaminateion of the composite laminate under high velocity impact. The 3D-Hashin failure criteria were used to predict the in-plane failure of composite by replacing quasi-static strength properties with rate-dependent strength properties. By using a degradation constitutive model, the main damage modes of the composite laminates which were delamination, matrix crack and fiber breakage were simulated. Parametric studies show that the prediction of the residual velocities agree well with the experimental results, and reducing diameter of the projectile or increasing ply angle and target thickness will reduce the damage area of the composite laminates under high velocity impact.
A 3D rate-dependent constitutive model was developed to simulate damage of laminated polymer matrix composites under high velocity impact. The cohesive elements were involved between two layers to simulate delaminateion of the composite laminate under high velocity impact. The 3D-Hashin failure criteria were used to predict the in-plane failure of composite by replacing quasi-static strength properties with rate-dependent strength properties. By using a degradation constitutive model, the main damage modes of the composite laminates which were delamination, matrix crack and fiber breakage were simulated. Parametric studies show that the prediction of the residual velocities agree well with the experimental results, and reducing diameter of the projectile or increasing ply angle and target thickness will reduce the damage area of the composite laminates under high velocity impact.
2012, 29(1): 162-168.
Abstract:
A visco-elastic model for fiber reinforced composites based on standard linear solid model was developed. Its governing equation as well as the formulae of relaxation modulus and creep compliance was deduced. The finite element method analysis testified that this model has a good accuracy. By virtue of this model, the effects of fiber geometric properties on relaxation modulus and creep compliance of the composite were also investigated. The results reveal that creep compliance of the composite is in a linear relation with fiber-matrix length ratio (FMLR). When fiber-matrix radius ratio (FMRR) exceeds a critical value, relaxation modulus and creep compliance change only slowly, and the critical value decreases with the increasing elastic modulus of fiber. Moreover, if fiber-matrix modulus ratio is quite large, fiber reinforcement-coefficient and compliance-coefficient are time independent.
A visco-elastic model for fiber reinforced composites based on standard linear solid model was developed. Its governing equation as well as the formulae of relaxation modulus and creep compliance was deduced. The finite element method analysis testified that this model has a good accuracy. By virtue of this model, the effects of fiber geometric properties on relaxation modulus and creep compliance of the composite were also investigated. The results reveal that creep compliance of the composite is in a linear relation with fiber-matrix length ratio (FMLR). When fiber-matrix radius ratio (FMRR) exceeds a critical value, relaxation modulus and creep compliance change only slowly, and the critical value decreases with the increasing elastic modulus of fiber. Moreover, if fiber-matrix modulus ratio is quite large, fiber reinforcement-coefficient and compliance-coefficient are time independent.
2012, 29(1): 169-175.
Abstract:
A model for the damage analysis of the open-hole tension composite laminates was developed. The model divided the failure modes of composite laminates into intra-laminar and inter-laminar damage. The model simulated damage initiation, damage progression, final damage and predicted failure mode and failure load of laminates with central circular holes subjected to tensile load based on progressive failure analysis methodology. The failure modes and failure loads of different laminates were predicted and compared with the experimental results. The results show that the model could predict the failure mode and failure load of open-hole tension laminates exactly.
A model for the damage analysis of the open-hole tension composite laminates was developed. The model divided the failure modes of composite laminates into intra-laminar and inter-laminar damage. The model simulated damage initiation, damage progression, final damage and predicted failure mode and failure load of laminates with central circular holes subjected to tensile load based on progressive failure analysis methodology. The failure modes and failure loads of different laminates were predicted and compared with the experimental results. The results show that the model could predict the failure mode and failure load of open-hole tension laminates exactly.
2012, 29(1): 176-182.
Abstract:
The tensile behavior of composite laminate containing penetrated damage and the optimization of repair designing parameters were studied after being flush repaired on double-sides. The results demonstrate that the recovery of failure strength of repairing specimens could reach 80% after double-sided flush repaired. The strength of repair specimens can be recovered to the maximum, when scarf ratio is 1∶40, and covering layers number is three with the layer's orientation is the same as the mother plate's layer which is close to covering layers. Double-sides flush repairing is familiar to any thicknesses and any lay-up ways of the mother laminates. A 3D finite element analysis was studied to verify the test result using ABAQUS software. In the model, every layer was set as a section, then give it the orientation of each layer. The analysis data are agree with the test results.
The tensile behavior of composite laminate containing penetrated damage and the optimization of repair designing parameters were studied after being flush repaired on double-sides. The results demonstrate that the recovery of failure strength of repairing specimens could reach 80% after double-sided flush repaired. The strength of repair specimens can be recovered to the maximum, when scarf ratio is 1∶40, and covering layers number is three with the layer's orientation is the same as the mother plate's layer which is close to covering layers. Double-sides flush repairing is familiar to any thicknesses and any lay-up ways of the mother laminates. A 3D finite element analysis was studied to verify the test result using ABAQUS software. In the model, every layer was set as a section, then give it the orientation of each layer. The analysis data are agree with the test results.
2012, 29(1): 183-189.
Abstract:
According to the problems that traditional time reversal (TR) method eliminates propagation time of Lamb waves and its procedure is complicated, a virtual time reversal (VTR) method is presented. In the method, changing-element exciting and receiving mechanism is adopted to reserve time information and the TR procedure is replaced by the signal operations. The realization involving acquiring transfer functions of damage detecting path under step pulse excitation is discussed. A high-resolution damage imaging method based on VTR is developed. To reduce the anisotropic effect in composite plates, velocity correction is carried out during the imaging. The experimental results show that damage scattered wavepackets of Lamb waves in the carbon fiber composite plate can be partly recompressed and time reversal focused by VTR. Both the signal damage and dual adjacent ones in the plate are clearly displayed by the proposed imaging method.
According to the problems that traditional time reversal (TR) method eliminates propagation time of Lamb waves and its procedure is complicated, a virtual time reversal (VTR) method is presented. In the method, changing-element exciting and receiving mechanism is adopted to reserve time information and the TR procedure is replaced by the signal operations. The realization involving acquiring transfer functions of damage detecting path under step pulse excitation is discussed. A high-resolution damage imaging method based on VTR is developed. To reduce the anisotropic effect in composite plates, velocity correction is carried out during the imaging. The experimental results show that damage scattered wavepackets of Lamb waves in the carbon fiber composite plate can be partly recompressed and time reversal focused by VTR. Both the signal damage and dual adjacent ones in the plate are clearly displayed by the proposed imaging method.
2012, 29(1): 190-195.
Abstract:
The effective anti-plane shear modulus was studied for the composites containing hollow nano inclusion. Based on the theory of Gurtin-Murdoch surface/interface theory and the generalized self-consistent method, the rigorous whole-field solution is obtained for the void-inclusion-matrix-equivalent medium model. The closed-form solution of the effective anti-plane shear modulus of the hollow nano inclusion composites is presented. Many significant solutions can be regarded as special or degenerated cases. The numerical results reveal that the effective anti-plane shear modulus is influenced remarkably when the size of the hollow nano inclusion is on the order of nanometer. With the increase of the size of the hollow nano inclusion, the surface/interface effect abates gradually. For the same volume fraction and outer radius of the hollow nano inclusion, the thinner the wall thickness is, the greater of the surface/interface effect is. The surface/interface effect of the hollow nano composites is much larger than that of the solid nano composites for the same outer radius of the inclusion. The effective anti-plane shear modulus of the hollow nano composites depends strongly on the surface/interface property and the stiffness of the inclusion. A very hard inclusion shields the surface/interface effect.
The effective anti-plane shear modulus was studied for the composites containing hollow nano inclusion. Based on the theory of Gurtin-Murdoch surface/interface theory and the generalized self-consistent method, the rigorous whole-field solution is obtained for the void-inclusion-matrix-equivalent medium model. The closed-form solution of the effective anti-plane shear modulus of the hollow nano inclusion composites is presented. Many significant solutions can be regarded as special or degenerated cases. The numerical results reveal that the effective anti-plane shear modulus is influenced remarkably when the size of the hollow nano inclusion is on the order of nanometer. With the increase of the size of the hollow nano inclusion, the surface/interface effect abates gradually. For the same volume fraction and outer radius of the hollow nano inclusion, the thinner the wall thickness is, the greater of the surface/interface effect is. The surface/interface effect of the hollow nano composites is much larger than that of the solid nano composites for the same outer radius of the inclusion. The effective anti-plane shear modulus of the hollow nano composites depends strongly on the surface/interface property and the stiffness of the inclusion. A very hard inclusion shields the surface/interface effect.
2012, 29(1): 196-206.
Abstract:
A general theory for hygrothermal elastic anisotropic damaged composites was developed on the theoretical basis of irreversible thermodynamics without any hypothesis. The constitutive functional expansion method was used for damage constitutive equation. All of the general representations of constitutive equations for hygrothermal elastic damaged materials were derived. These constitutive equations included specific free energy density expression, stress-strain relation, entropy density equation, damage strain energy release rate expression, hygroscopic dual force expression, hygro-thermo-stress-damage coupled heat conduction equation and damage evolution equations. The results show that there are several damage effect functions in constitutive equations, which indicate the influences of damage on the macroscopic mechanics properties and hygrothermal properties of materials. The detailed expressions of the damage effect functions could be determined by micromechanics, which relate the continuum damage mechanics with the microscopic damage mechanics. Finally, the determination methods of damage effect functions and coefficient tensors were illustrated from two aspects of micromechanics and experimental observations, which provided important theory basis for analyzing damage problems of composites under the variable temperature and humidity circumstances.
A general theory for hygrothermal elastic anisotropic damaged composites was developed on the theoretical basis of irreversible thermodynamics without any hypothesis. The constitutive functional expansion method was used for damage constitutive equation. All of the general representations of constitutive equations for hygrothermal elastic damaged materials were derived. These constitutive equations included specific free energy density expression, stress-strain relation, entropy density equation, damage strain energy release rate expression, hygroscopic dual force expression, hygro-thermo-stress-damage coupled heat conduction equation and damage evolution equations. The results show that there are several damage effect functions in constitutive equations, which indicate the influences of damage on the macroscopic mechanics properties and hygrothermal properties of materials. The detailed expressions of the damage effect functions could be determined by micromechanics, which relate the continuum damage mechanics with the microscopic damage mechanics. Finally, the determination methods of damage effect functions and coefficient tensors were illustrated from two aspects of micromechanics and experimental observations, which provided important theory basis for analyzing damage problems of composites under the variable temperature and humidity circumstances.
2012, 29(1): 207-211.
Abstract:
A numerical simulation for bending-twisting coupling deformation of unsymmetrical and unbalanced composite laminates under bending load was conducted. The parameters such as laminate width and thickness were also studied. Based on the simulation results, a flexible support device for the four-point-bending test was developed. The flexible four-point-bending tests for unsymmetrical and unbalanced composite laminates were conducted. The test results show that the developed flexible four-point-bending support device does not constrain the twisting deformation of laminates while applying bending load to it. The flexible four-point-bending support device is capable of measuring bending-twisting coupling coefficient of unsymmetrical and unbalanced composite laminates.
A numerical simulation for bending-twisting coupling deformation of unsymmetrical and unbalanced composite laminates under bending load was conducted. The parameters such as laminate width and thickness were also studied. Based on the simulation results, a flexible support device for the four-point-bending test was developed. The flexible four-point-bending tests for unsymmetrical and unbalanced composite laminates were conducted. The test results show that the developed flexible four-point-bending support device does not constrain the twisting deformation of laminates while applying bending load to it. The flexible four-point-bending support device is capable of measuring bending-twisting coupling coefficient of unsymmetrical and unbalanced composite laminates.
2012, 29(1): 212-216.
Abstract:
A point of view that the carbon fiber has composite structure is proposed. The relationship between the practical elasticity coefficient of carbon fiber and the crystallinity, micro-fiber orientation and pore conditions was researched based on the micro mechanics theory for mechanical properties of composite materials, the continuous fiber reinforced single plate principle and the properties of microstructure of carbon fiber. The analyzing and calculating methods were obtained, and the main factors which affect the elasticity coefficient were found. A innovative theoretical analysis method and the definite calculation formula were given. The obtained theoretical results are consistent with the experimental results. It is revealed that the pore density, the fiber size and orientation, the crystallinity determine the elasticity coefficient of carbon fiber, which provides theoretical basis to improve the carbon fiber production process.
A point of view that the carbon fiber has composite structure is proposed. The relationship between the practical elasticity coefficient of carbon fiber and the crystallinity, micro-fiber orientation and pore conditions was researched based on the micro mechanics theory for mechanical properties of composite materials, the continuous fiber reinforced single plate principle and the properties of microstructure of carbon fiber. The analyzing and calculating methods were obtained, and the main factors which affect the elasticity coefficient were found. A innovative theoretical analysis method and the definite calculation formula were given. The obtained theoretical results are consistent with the experimental results. It is revealed that the pore density, the fiber size and orientation, the crystallinity determine the elasticity coefficient of carbon fiber, which provides theoretical basis to improve the carbon fiber production process.
