2005 Vol. 22, No. 5
2005, 22(5): 1-8.
Abstract:
The studies done by domestic and foreign scholars on the mechanical behavior of fiber reinforced foams are reviewed briefly in this paper. The fabrication technique and microstructure of fiber reinforced foams are introduced simply. The mechanical properties of the materials and some works of the authors are reported emphatically. The basic mechanical properties, reinforcement and failure mechanisms, effect of temperature, the length of fiber and the influence of the fraction of components and surface treatment on the mechanical behavior are included. The research trends of this kind of materials in the future are prospected.
The studies done by domestic and foreign scholars on the mechanical behavior of fiber reinforced foams are reviewed briefly in this paper. The fabrication technique and microstructure of fiber reinforced foams are introduced simply. The mechanical properties of the materials and some works of the authors are reported emphatically. The basic mechanical properties, reinforcement and failure mechanisms, effect of temperature, the length of fiber and the influence of the fraction of components and surface treatment on the mechanical behavior are included. The research trends of this kind of materials in the future are prospected.
2005, 22(5): 9-15.
Abstract:
The application progress, dielectric mechanism, choice of raw materials and preparation process are reviewed for inorganic/organic functional composites with high dielectric constant at high temperature. The key is focused on the new development direction and design of some new materials according to the mechanism of high dielectric. It is pointed out that the choice and modification of fillers and polymer matrix are very important. And it is also crucial to improve phase interfaces between the fillers and ploymers and modify the surface of nanosize fillers.
The application progress, dielectric mechanism, choice of raw materials and preparation process are reviewed for inorganic/organic functional composites with high dielectric constant at high temperature. The key is focused on the new development direction and design of some new materials according to the mechanism of high dielectric. It is pointed out that the choice and modification of fillers and polymer matrix are very important. And it is also crucial to improve phase interfaces between the fillers and ploymers and modify the surface of nanosize fillers.
2005, 22(5): 16-24.
Abstract:
The reasonability and reliability of a rigid-plastic meso-damage constitutive theory were examined for porous composites reinforced by rigid particles. The numerical calculations based on the constitutive theory were compared with the tensile experiments on Al matrix composites reinforced by SiC particles. The results show that the constitutive theory agrees with the experimental stress-strain curves, so this constitutive theory can be put into numerical simulation and predict the mechanics properties of the composites reinforced by rigid particles. Based on the above, the ductility and evolution law for void and particles were discussed in this paper.
The reasonability and reliability of a rigid-plastic meso-damage constitutive theory were examined for porous composites reinforced by rigid particles. The numerical calculations based on the constitutive theory were compared with the tensile experiments on Al matrix composites reinforced by SiC particles. The results show that the constitutive theory agrees with the experimental stress-strain curves, so this constitutive theory can be put into numerical simulation and predict the mechanics properties of the composites reinforced by rigid particles. Based on the above, the ductility and evolution law for void and particles were discussed in this paper.
2005, 22(5): 25-30.
Abstract:
ZrV2O7 with negative-thermal-expansion(NTE)was prepared by calcined-synthesis combined with wet-chemical process. The interface behaviors and thermal expansion character of ZrV2O7/Al composites were studied by powdermetallurgy. The results of XRD show that the samples with calcined-synthesis combined with wet-chemical process almost contain single phase of ZrV2O7. The results of XRD,SEM and EPS demonstrate that ZrV2O7/Al composites made by different press-formed and sintered-synthesis techniques have good sintered and dipped characters in a certain scope of sintered-temperature, whether they are in solid-state or molt-state. But the more reactive Al3+can displace with the Zr4+ ions and the reaction degrees will increase with sintered-temperature. The results of dilatometer show that ZrV2O7 has a strong isotropic and stable NTE property from 400K up to 680K and ZrV2O7/Al composites with good mould and fine structure were obtained by powder metallurgy technique. At the same time, the coefficient of thermal expansion of ZrV2O7/Al composites is lower than that of Al, though the coefficient of composites was also positive.
ZrV2O7 with negative-thermal-expansion(NTE)was prepared by calcined-synthesis combined with wet-chemical process. The interface behaviors and thermal expansion character of ZrV2O7/Al composites were studied by powdermetallurgy. The results of XRD show that the samples with calcined-synthesis combined with wet-chemical process almost contain single phase of ZrV2O7. The results of XRD,SEM and EPS demonstrate that ZrV2O7/Al composites made by different press-formed and sintered-synthesis techniques have good sintered and dipped characters in a certain scope of sintered-temperature, whether they are in solid-state or molt-state. But the more reactive Al3+can displace with the Zr4+ ions and the reaction degrees will increase with sintered-temperature. The results of dilatometer show that ZrV2O7 has a strong isotropic and stable NTE property from 400K up to 680K and ZrV2O7/Al composites with good mould and fine structure were obtained by powder metallurgy technique. At the same time, the coefficient of thermal expansion of ZrV2O7/Al composites is lower than that of Al, though the coefficient of composites was also positive.
2005, 22(5): 31-38.
Abstract:
The influence of particle size on the dynamic behavior of particle-reinforced metal-matrix composites was investigated through the finite element method under different strain rates. The three-dimensional cubic unit cell models which contained one or several SiC particles were employed. The diameters of the particles were 16 μ m and 7.5 μ m, separately. And the arrangement of the multi-particles inside the unit cell mode was random. The stress-strain behavior of the matrix material is assumed to be power-law strain hardening and coupled with power-law strain rate hardening. The simulation results show that the influence of particle size on the dynamic behavior of PMMCs is coupled with the volume fraction of the particle and the strain rate. The smaller the diameter of the particle, the better the reinforced effect, when the volume fraction of the particles is constant. The flow stress increases with the increasing of the particle volume fraction and strain rates.
The influence of particle size on the dynamic behavior of particle-reinforced metal-matrix composites was investigated through the finite element method under different strain rates. The three-dimensional cubic unit cell models which contained one or several SiC particles were employed. The diameters of the particles were 16 μ m and 7.5 μ m, separately. And the arrangement of the multi-particles inside the unit cell mode was random. The stress-strain behavior of the matrix material is assumed to be power-law strain hardening and coupled with power-law strain rate hardening. The simulation results show that the influence of particle size on the dynamic behavior of PMMCs is coupled with the volume fraction of the particle and the strain rate. The smaller the diameter of the particle, the better the reinforced effect, when the volume fraction of the particles is constant. The flow stress increases with the increasing of the particle volume fraction and strain rates.
2005, 22(5): 39-46.
Abstract:
Different components of 316L stainless steel(316L SS)fibre/HA biomaterials and 316L SS fibre/HA-ZrO2 (CaO )biomaterials were fabricated with vacuum sintering. Metallographical microscope, SEM and EDXA analysis were carried out to investigate the microstructure, fracture property and microfield element contents of the composites. The results show that 316L SS fibres and nano-sized ZrO2 (CaO )have reinforcing and toughening effects on the composites. Comprehensive consideration suggests that 316L SS fibre/HA-ZrO2 (CaO) biomaterials with 20% 316L SS fibre have optimal mechanical properties with bending strength and compressive strength of 140.1MPa and 348.9MPa. Bending strength increases with decreasing diameter or length of the 316L SS fibres. Microstructure of the composites changes regularly with the ratio between HA and 316L SS fibre. No obvious flaws or pores appear in the composites and 316L SS fibre is enwrapped in the HA (ZrO2 )matrix with tight integration. Brittle fracture appears in 5% 316L SS fibre/HA-ZrO2 (CaO )biomaterials and tough fracture appears in 10%, 20%, 40% 316L SS fibre/HA-ZrO2 (CaO )biomaterials. And the toughness increases with the rise of 316L SS fibre contents in 316L SS fibre/HA-ZrO2 (CaO) biomaterials with 10%, 20%, 40% 316L SS fibres. Some Fe element diffusion of the toughened phase takes place in the HA (ZrO2 )matrix and no Ca, P element diffusion in 316L SS fibre. Both matrix and toughened phase are relatively independent and no chemical reaction is observed in the composites.
Different components of 316L stainless steel(316L SS)fibre/HA biomaterials and 316L SS fibre/HA-ZrO2 (CaO )biomaterials were fabricated with vacuum sintering. Metallographical microscope, SEM and EDXA analysis were carried out to investigate the microstructure, fracture property and microfield element contents of the composites. The results show that 316L SS fibres and nano-sized ZrO2 (CaO )have reinforcing and toughening effects on the composites. Comprehensive consideration suggests that 316L SS fibre/HA-ZrO2 (CaO) biomaterials with 20% 316L SS fibre have optimal mechanical properties with bending strength and compressive strength of 140.1MPa and 348.9MPa. Bending strength increases with decreasing diameter or length of the 316L SS fibres. Microstructure of the composites changes regularly with the ratio between HA and 316L SS fibre. No obvious flaws or pores appear in the composites and 316L SS fibre is enwrapped in the HA (ZrO2 )matrix with tight integration. Brittle fracture appears in 5% 316L SS fibre/HA-ZrO2 (CaO )biomaterials and tough fracture appears in 10%, 20%, 40% 316L SS fibre/HA-ZrO2 (CaO )biomaterials. And the toughness increases with the rise of 316L SS fibre contents in 316L SS fibre/HA-ZrO2 (CaO) biomaterials with 10%, 20%, 40% 316L SS fibres. Some Fe element diffusion of the toughened phase takes place in the HA (ZrO2 )matrix and no Ca, P element diffusion in 316L SS fibre. Both matrix and toughened phase are relatively independent and no chemical reaction is observed in the composites.
2005, 22(5): 47-51.
Abstract:
Two types of coatings were prepared on the surface of aligned carbon nanotubes on AAO(Aluminum anodic oxide)template, CuPc coating by vacuum thermal deposition and cobalt coating by electrodeposition. Observations by SEM and TEM show that organic and inorganic coatings are obtained on the aligned carbon nanotubes. There is still a little difference between them: the back surface of carbon nanotubes has no film with the vacuum thermal deposition while the whole surface of nanotubes is coated with the electrodeposition method.
Two types of coatings were prepared on the surface of aligned carbon nanotubes on AAO(Aluminum anodic oxide)template, CuPc coating by vacuum thermal deposition and cobalt coating by electrodeposition. Observations by SEM and TEM show that organic and inorganic coatings are obtained on the aligned carbon nanotubes. There is still a little difference between them: the back surface of carbon nanotubes has no film with the vacuum thermal deposition while the whole surface of nanotubes is coated with the electrodeposition method.
2005, 22(5): 52-59.
Abstract:
Expandable graphite was added to APP/PER/EN system to get a new kind of EG modified flame re-tardant coating. The thermal degradation, element content in residue char, char formation rate, heat insulation property of APP/PER/EN coating and EG modified flame retardant coatings were studied by using DTA, TG, SEM, EDS and heat insulation experiment. The temperature range of chemical expanding reaction among APP, PER and EN is near to that of a physical expanding process of expandable graphite, so the two processes can have good synergic effect. Expandable graphite can greatly improve the char formation rate, antioxidation and heat stability of a char layer. Too high content of EG (≥15%) makes the char layer easily detached from the substrate. 10% EG(mass fraction) can efficiently improve heat insulation and flame retardant properties of the APP/PER/EN coating.
Expandable graphite was added to APP/PER/EN system to get a new kind of EG modified flame re-tardant coating. The thermal degradation, element content in residue char, char formation rate, heat insulation property of APP/PER/EN coating and EG modified flame retardant coatings were studied by using DTA, TG, SEM, EDS and heat insulation experiment. The temperature range of chemical expanding reaction among APP, PER and EN is near to that of a physical expanding process of expandable graphite, so the two processes can have good synergic effect. Expandable graphite can greatly improve the char formation rate, antioxidation and heat stability of a char layer. Too high content of EG (≥15%) makes the char layer easily detached from the substrate. 10% EG(mass fraction) can efficiently improve heat insulation and flame retardant properties of the APP/PER/EN coating.
2005, 22(5): 60-63.
Abstract:
The effects of ultraviolet light intensity on the structure and properties of HDPE were studied. Some oxygen containing groups such as C—O, C O and C ( O) O were introduced onto the HDPE chains by ultraviolet irradiation in air without adding any additives. These groups content and gel contents in the irradiated HDPE increase with the irradiation light intensity under the same irradiation time and environmental temperature. Under the ultraviolet light intensity, the crystal style and cell parameter of irradiated HDPE remain unchanged; the melting temperature and water contact angle of HDPE decrease, while the degree of crystallinity increases, and their variation amplitude increases with the ultraviolet light intensity. Compared with those of HDPE/PVA composites, the mechanical properties of HDPE/PVA composites compatibilized with irradiated HDPE increased. The compatibilization of HDPE irradiated at high ultraviolet light intensity in HDPE/PVA composites is better than that at low ultraviolet light intensity.
The effects of ultraviolet light intensity on the structure and properties of HDPE were studied. Some oxygen containing groups such as C—O, C O and C ( O) O were introduced onto the HDPE chains by ultraviolet irradiation in air without adding any additives. These groups content and gel contents in the irradiated HDPE increase with the irradiation light intensity under the same irradiation time and environmental temperature. Under the ultraviolet light intensity, the crystal style and cell parameter of irradiated HDPE remain unchanged; the melting temperature and water contact angle of HDPE decrease, while the degree of crystallinity increases, and their variation amplitude increases with the ultraviolet light intensity. Compared with those of HDPE/PVA composites, the mechanical properties of HDPE/PVA composites compatibilized with irradiated HDPE increased. The compatibilization of HDPE irradiated at high ultraviolet light intensity in HDPE/PVA composites is better than that at low ultraviolet light intensity.
2005, 22(5): 64-71.
Abstract:
Energy dispersive X-ray spectroscopy (EDX) is a kind of analysis method used in researching the adhesive joint and polymer composite surface and interface characters The changes of the adhesive/carbon-carbon composite joint surface and interface at different temperatures were researched by EDX The results indicate that carbon element content on C-C composite surface in Z direction is less than that in X and Y directions from room temperature to 900℃, which was decided by the characters of C-C composite The break form of the adhesive/carbon-carbon composite joint is changed from C-C composite break at room temperature into adhesive break at higher than 200℃ The changes of carbon, oxygen and silicon elements content on the adhesive and C-C composites surface indicate that the heat decomposition speed of the adhesive is almost the same as that of C-C composite under 550℃，but above 550℃ the adhesive decomposition speed is faster than that of C-C composites
Energy dispersive X-ray spectroscopy (EDX) is a kind of analysis method used in researching the adhesive joint and polymer composite surface and interface characters The changes of the adhesive/carbon-carbon composite joint surface and interface at different temperatures were researched by EDX The results indicate that carbon element content on C-C composite surface in Z direction is less than that in X and Y directions from room temperature to 900℃, which was decided by the characters of C-C composite The break form of the adhesive/carbon-carbon composite joint is changed from C-C composite break at room temperature into adhesive break at higher than 200℃ The changes of carbon, oxygen and silicon elements content on the adhesive and C-C composites surface indicate that the heat decomposition speed of the adhesive is almost the same as that of C-C composite under 550℃，but above 550℃ the adhesive decomposition speed is faster than that of C-C composites
2005, 22(5): 72-77.
Abstract:
The preparation technology and performances of carbon nanotubes/natural rubber composites were studied. After the carbon nanotubes were added into natural rubber matrix, the area of crystal-melting peak of DSC curve of rubber decreases. At the same time, the scorch time of rubber shortens slightly, and the curing reversion reduces. The dispersing of carbon nanotubes in rubber and the adhesion between carbon nanotubes and rubber are improved after being treated with the dispersing-bonding system. The mechanical properties of carbon nanotubes composites increase. The rebound degree and the dynamic compress properties of carbon nanotubes composites are more superior to those of natural rubber filled with carbon black. Compared with the sample filled with carbon black, the storage modulus and the glass transition temperature of carbon nanotubes reinforced composites are higher, and the thermal stability is also preferable.
The preparation technology and performances of carbon nanotubes/natural rubber composites were studied. After the carbon nanotubes were added into natural rubber matrix, the area of crystal-melting peak of DSC curve of rubber decreases. At the same time, the scorch time of rubber shortens slightly, and the curing reversion reduces. The dispersing of carbon nanotubes in rubber and the adhesion between carbon nanotubes and rubber are improved after being treated with the dispersing-bonding system. The mechanical properties of carbon nanotubes composites increase. The rebound degree and the dynamic compress properties of carbon nanotubes composites are more superior to those of natural rubber filled with carbon black. Compared with the sample filled with carbon black, the storage modulus and the glass transition temperature of carbon nanotubes reinforced composites are higher, and the thermal stability is also preferable.
2005, 22(5): 78-82.
Abstract:
PZN-PZT/PI,PZN-PZT/PVDF 0-3 piezoelectric composites were fabricated using solution blended and hot pressing processes. The piezoelectric constant d33 and flexibility of the materials are excellent. The common character of 0-3 piezoelectric ceramic/polymer composites was discussed. The dependence of type and mass fraction of ceramic powder, type of polymer and poling parameters on the piezoelectric coefficient d33 of piezoelectric composites was investigated. Some methods to improve the piezoelectric property of this kind of material were approached.
PZN-PZT/PI,PZN-PZT/PVDF 0-3 piezoelectric composites were fabricated using solution blended and hot pressing processes. The piezoelectric constant d33 and flexibility of the materials are excellent. The common character of 0-3 piezoelectric ceramic/polymer composites was discussed. The dependence of type and mass fraction of ceramic powder, type of polymer and poling parameters on the piezoelectric coefficient d33 of piezoelectric composites was investigated. Some methods to improve the piezoelectric property of this kind of material were approached.
2005, 22(5): 83-88.
Abstract:
Capillary impregnation of pure resins in the transverse direction of unidirectional cloth beds was studied elementarily by using self-designed fiber holder. The effect of experiment parameters, such as temperature, fiber volume fraction, fiber types and the stacking orientation of unidirectional cloth on the velocity of the capillary impregnation was investigated. And the impregnation of the unidirectional cloth without sizing on the surface was tested. In comparison with the cloths with sizing, the capillary impregnation velocity of clothes without sizing appears to be much quick. The results show that increasing the temperature and decreasing the fiber volume fraction can both improve the velocity of impregnation. However, changing the stacking orientation of the unidirectional cloth has little influence on the impregnation behavior.
Capillary impregnation of pure resins in the transverse direction of unidirectional cloth beds was studied elementarily by using self-designed fiber holder. The effect of experiment parameters, such as temperature, fiber volume fraction, fiber types and the stacking orientation of unidirectional cloth on the velocity of the capillary impregnation was investigated. And the impregnation of the unidirectional cloth without sizing on the surface was tested. In comparison with the cloths with sizing, the capillary impregnation velocity of clothes without sizing appears to be much quick. The results show that increasing the temperature and decreasing the fiber volume fraction can both improve the velocity of impregnation. However, changing the stacking orientation of the unidirectional cloth has little influence on the impregnation behavior.
2005, 22(5): 89-93.
Abstract:
Polymer of methyl-di-phenylacetylene-silane (MDPES) possesses excellent properties of high temperature-resistance, low dielectric dissipation fraction, etc, but its mechanical property is not significant for its poor bonding with glass-fiber. The di-N-m-acetylene-phenylphthalimide-ether(DAIE) was added into MDPES to modify its properties through copolymerization. To research copolymerization of DAIE and MDPES at different mass ratios, it was found that when MDAIE/MMDPES was 4∶5, the value of Td5 ( temperature of 5% weight loss) is 467℃ in nitrogen; its mass residual ratio is 82.7% based on the initial mass at 800℃ in nitrogen; the flexural strength at room temperature is 274MPa; the flexural strength at 235℃ is 241MPa; the flexural strength retention at 235℃ is 88.5%; its permittivity is 4.18 and tanδ is 2.5×10-3 in the frequency of 1MHz.
Polymer of methyl-di-phenylacetylene-silane (MDPES) possesses excellent properties of high temperature-resistance, low dielectric dissipation fraction, etc, but its mechanical property is not significant for its poor bonding with glass-fiber. The di-N-m-acetylene-phenylphthalimide-ether(DAIE) was added into MDPES to modify its properties through copolymerization. To research copolymerization of DAIE and MDPES at different mass ratios, it was found that when MDAIE/MMDPES was 4∶5, the value of Td5 ( temperature of 5% weight loss) is 467℃ in nitrogen; its mass residual ratio is 82.7% based on the initial mass at 800℃ in nitrogen; the flexural strength at room temperature is 274MPa; the flexural strength at 235℃ is 241MPa; the flexural strength retention at 235℃ is 88.5%; its permittivity is 4.18 and tanδ is 2.5×10-3 in the frequency of 1MHz.
2005, 22(5): 94-99.
Abstract:
A glass fabric/polyvinyl chloride (PVC) composite material with super thin thickness, lightweight and toughness, was manufactured with the infusion technology under normal pressure. The sound insulation performance of this novel material was determined with a two-channel acoustic analyzer. The structure and mechanical properties were also investigated via SEM, DMA, etc. The results show that the sound insulation properties of the composite material are better than those of the materials with single components, and the loss of the sound transmission through this material exceeds that predicted by the mass law, indicating the composite’s good sound insulation properties.
A glass fabric/polyvinyl chloride (PVC) composite material with super thin thickness, lightweight and toughness, was manufactured with the infusion technology under normal pressure. The sound insulation performance of this novel material was determined with a two-channel acoustic analyzer. The structure and mechanical properties were also investigated via SEM, DMA, etc. The results show that the sound insulation properties of the composite material are better than those of the materials with single components, and the loss of the sound transmission through this material exceeds that predicted by the mass law, indicating the composite’s good sound insulation properties.
2005, 22(5): 100-106.
Abstract:
In order to further improve the mechanical properties of commercial plastics polypropylene (PP), PP composite material incorporated with the surface-modified nano-TiO2 particles by titanium-acid ester coupling agent NDZ-201 was prepared through the blending method. The effect of the mass fraction of TiO2 and the dosage of NDZ-201 on the toughening and strengthening of PP matrix was investigated based on the results of the differential scanning calorimeter (DSC) and the observation of the impact fractography of the material. It was shown that the flexural strength, the modulus and the impact strength of the nanocomposite were obviously improved with the increasing of nano-TiO2 percentage (less than 5%); and the augment of the properties dropped and turned to a decreasing tendency with the further supplement of the nano-TiO2 content. It was also found that the addition of nano-TiO2 promoted the crystallization of PP, leading to a much more quantity of finer β grains. Moreover, the homogeneous dispersion of nano-TiO2 particles enhanced the obstruction to the cracks’ propagating in PP. It was indicated that the dosage of titanium-acid ester coupling agent had a parabola-like relation with the mechanical properties of nano-TiO2/PP composite at a fixed nano-TiO2 content, while the optimal toughening and strengthening effect could be achieved at 2% of NDZ-201.
In order to further improve the mechanical properties of commercial plastics polypropylene (PP), PP composite material incorporated with the surface-modified nano-TiO2 particles by titanium-acid ester coupling agent NDZ-201 was prepared through the blending method. The effect of the mass fraction of TiO2 and the dosage of NDZ-201 on the toughening and strengthening of PP matrix was investigated based on the results of the differential scanning calorimeter (DSC) and the observation of the impact fractography of the material. It was shown that the flexural strength, the modulus and the impact strength of the nanocomposite were obviously improved with the increasing of nano-TiO2 percentage (less than 5%); and the augment of the properties dropped and turned to a decreasing tendency with the further supplement of the nano-TiO2 content. It was also found that the addition of nano-TiO2 promoted the crystallization of PP, leading to a much more quantity of finer β grains. Moreover, the homogeneous dispersion of nano-TiO2 particles enhanced the obstruction to the cracks’ propagating in PP. It was indicated that the dosage of titanium-acid ester coupling agent had a parabola-like relation with the mechanical properties of nano-TiO2/PP composite at a fixed nano-TiO2 content, while the optimal toughening and strengthening effect could be achieved at 2% of NDZ-201.
2005, 22(5): 107-112.
Abstract:
To achieve the interlaminar tensile properties for a kind of carbon fiber two-dimensional orthogonal plain woven reinforced polymer matrix composite, numbers of quasistatic and dynamic tensile experiments in the through-thickness direction of the composite were conducted, by means of Instron apparatus and SHTB technology respectively. The tensile stress-strain curves and tensile strength were achieved in a large strain rate range ( from 10-3/s to 3×102/s). The experimental results show that the failure is bound to occur at the interlaminar of neighbouring carbon cloth. The tensile modulus and tensile strength increase slightly under impact loading, and the tensile failure strain is nearly independent of the strain rate.
To achieve the interlaminar tensile properties for a kind of carbon fiber two-dimensional orthogonal plain woven reinforced polymer matrix composite, numbers of quasistatic and dynamic tensile experiments in the through-thickness direction of the composite were conducted, by means of Instron apparatus and SHTB technology respectively. The tensile stress-strain curves and tensile strength were achieved in a large strain rate range ( from 10-3/s to 3×102/s). The experimental results show that the failure is bound to occur at the interlaminar of neighbouring carbon cloth. The tensile modulus and tensile strength increase slightly under impact loading, and the tensile failure strain is nearly independent of the strain rate.
2005, 22(5): 113-119.
Abstract:
The effect of maleic anhydride (MAH) grafted POE (Polyolefin Elastomer) on the morphology, microstructure and mechanical properties of PA66/POE blends was investigated by means of SEM, TEM, DSC and mechanical properties measurement. The results show that the grafted product (POE-g-MAH) can improve the miscibility between PA66 and POE, decrease the particle size of dispersion phase and obviously increase the charpy notched impact strength of these blends. It was found that there are more regular structures in the dispersion phase elastomer particles of PA66/POE-g-MAH blends than those in the particles of PA66/POE blends; the dispersion phase elastomer particles of PA66/POE-g-MAH blends can accelerate crystallization of the matrix, and increase the crystallization temperature Tcd and the crystallization enthalpy ΔHc of the PA66 matrix. In the case when the brittle-ductile transition of the blend occurs, the accelerating action reaches the strongest, and the values of Tcd and ΔHc reach maximum; the faster the cooling rate of the melt specimens, the stronger the accelerating action of the particles.
The effect of maleic anhydride (MAH) grafted POE (Polyolefin Elastomer) on the morphology, microstructure and mechanical properties of PA66/POE blends was investigated by means of SEM, TEM, DSC and mechanical properties measurement. The results show that the grafted product (POE-g-MAH) can improve the miscibility between PA66 and POE, decrease the particle size of dispersion phase and obviously increase the charpy notched impact strength of these blends. It was found that there are more regular structures in the dispersion phase elastomer particles of PA66/POE-g-MAH blends than those in the particles of PA66/POE blends; the dispersion phase elastomer particles of PA66/POE-g-MAH blends can accelerate crystallization of the matrix, and increase the crystallization temperature Tcd and the crystallization enthalpy ΔHc of the PA66 matrix. In the case when the brittle-ductile transition of the blend occurs, the accelerating action reaches the strongest, and the values of Tcd and ΔHc reach maximum; the faster the cooling rate of the melt specimens, the stronger the accelerating action of the particles.
2005, 22(5): 120-124.
Abstract:
3D-Cf/SiC composites were prepared with low-molecular polycarbosilane (PCS) using a precursor infiltration pyrolysis (PIP) process.The average molecular weight of active PCS is 400 (Mn) . The ceramic yield is approximately 70%, and PCS was translated into β-SiC crystal at 1200℃. The samples of 3D-Cf/SiC composites were prepared at three different heating rates.Bending strengthes were respectively 745.2MPa,686.7MPa,and 762.5MPa.SEM photographs of sample fracture surfaces indicate that in the micro-structures there are long fibers pulled out,and the fracture toughness is high.The matrix is close-grained.The research indicates that 3D-Cf/SiC composites with low-molecular polycarbosilane have good mechanical performance,and the low-molecular PCS fits the preparation of 3D-Cf/SiC composites by PIP process.
3D-Cf/SiC composites were prepared with low-molecular polycarbosilane (PCS) using a precursor infiltration pyrolysis (PIP) process.The average molecular weight of active PCS is 400 (Mn) . The ceramic yield is approximately 70%, and PCS was translated into β-SiC crystal at 1200℃. The samples of 3D-Cf/SiC composites were prepared at three different heating rates.Bending strengthes were respectively 745.2MPa,686.7MPa,and 762.5MPa.SEM photographs of sample fracture surfaces indicate that in the micro-structures there are long fibers pulled out,and the fracture toughness is high.The matrix is close-grained.The research indicates that 3D-Cf/SiC composites with low-molecular polycarbosilane have good mechanical performance,and the low-molecular PCS fits the preparation of 3D-Cf/SiC composites by PIP process.
2005, 22(5): 125-129.
Abstract:
Needled carbon cloth reinforced carbon/carbon (C/C) composite materials were improved by using the combination process of chemical vapor infiltration of carbon and direct reaction of silicon vapor with carbon at high temperature named as chemical vapor reaction (CVR) method to form SiC. Oxidation behavior of the obtained composites with various densities and open porosity was studied by static oxidation tests. The results show that, after being oxidated at 1160℃±10℃ for 65mins, the mass loss of the composites with a density of 2.47g/cm3 is less than 2.6%, while that of the same-structured C/C composite with a density of 1.95g/cm3 is as high as 32%. Treatment by CVR method can significantly improve the oxidation resistance properties. However, when the density of the C/C/SiC composite is lower and open porosity is higher, the effect is similar with C/C composite due to no formation of a continual layer of dense SiO2 on the specimen surface.
Needled carbon cloth reinforced carbon/carbon (C/C) composite materials were improved by using the combination process of chemical vapor infiltration of carbon and direct reaction of silicon vapor with carbon at high temperature named as chemical vapor reaction (CVR) method to form SiC. Oxidation behavior of the obtained composites with various densities and open porosity was studied by static oxidation tests. The results show that, after being oxidated at 1160℃±10℃ for 65mins, the mass loss of the composites with a density of 2.47g/cm3 is less than 2.6%, while that of the same-structured C/C composite with a density of 1.95g/cm3 is as high as 32%. Treatment by CVR method can significantly improve the oxidation resistance properties. However, when the density of the C/C/SiC composite is lower and open porosity is higher, the effect is similar with C/C composite due to no formation of a continual layer of dense SiO2 on the specimen surface.
2005, 22(5): 130-133.
Abstract:
The flexural strength of a 3D Hi-Nicalon/SiC composite was tested using the three point bending method at room temperature and the strength distribution was studied based on Weibull distribution. A graphical method and the stepwise regression were applied to optimizing the estimated parameters. Furthermore, the validity of the assumed distribution was examined by the Kolmogorov test. The results indicate that the statistical distribution of 3D Hi-Nicalon/SiC is in agreement with a two-parameter Weibull distribution characterized by σu＝0 and the Weibull modulus, m=8. 1545. The strength distribution of the 3D Hi-Nicalon/SiC composite in the three point bending test can be accurately predicted using the gained two-parameter Weibull distribution.
The flexural strength of a 3D Hi-Nicalon/SiC composite was tested using the three point bending method at room temperature and the strength distribution was studied based on Weibull distribution. A graphical method and the stepwise regression were applied to optimizing the estimated parameters. Furthermore, the validity of the assumed distribution was examined by the Kolmogorov test. The results indicate that the statistical distribution of 3D Hi-Nicalon/SiC is in agreement with a two-parameter Weibull distribution characterized by σu＝0 and the Weibull modulus, m=8. 1545. The strength distribution of the 3D Hi-Nicalon/SiC composite in the three point bending test can be accurately predicted using the gained two-parameter Weibull distribution.
2005, 22(5): 134-140.
Abstract:
To construct neural-network response surfaces for composite structural optimal design, the Orthotropic Experimental Method(OEM)was used to select the most appropriate structural analysis sample points. The constructed response surfaces were used as the objective function or constraint conditions. Together with other conventional constraints, they form an optimization design model which can be solved by using genetic algorithm(GA) . This approach is highly applicable for complex composite structural design. Taking a hat-stiffened composite plate as example, the weight response surface was developed as the objective function, and strength and stability response surfaces as constraints; all these neural networks were trained by PATRAN/NASTRAN computation. The optimization results illustrate that it can significantly reduce the cycles of FEM analysis and achieve highly accurate response approximation results. And eventually, the approach can greatly raise the efficiency of the optimization process.
To construct neural-network response surfaces for composite structural optimal design, the Orthotropic Experimental Method(OEM)was used to select the most appropriate structural analysis sample points. The constructed response surfaces were used as the objective function or constraint conditions. Together with other conventional constraints, they form an optimization design model which can be solved by using genetic algorithm(GA) . This approach is highly applicable for complex composite structural design. Taking a hat-stiffened composite plate as example, the weight response surface was developed as the objective function, and strength and stability response surfaces as constraints; all these neural networks were trained by PATRAN/NASTRAN computation. The optimization results illustrate that it can significantly reduce the cycles of FEM analysis and achieve highly accurate response approximation results. And eventually, the approach can greatly raise the efficiency of the optimization process.
2005, 22(5): 141-146.
Abstract:
In order to optimize the designs and evaluate exactly the performances of PE/PE laminated composites, it is necessary to research the damage mechanisms of these materials, then to indicate the rules of the damage propagation, and to predict the effects on the various performances such as stiffness, strength and so on with the damage developing. A modified numerical model to simulate the mechanical behavior of PE/PE laminated composites was proposed based on the quasi-3-dimensional model concept. The damage propagation of three types of quasi-isotropic UHMWPE/HDPE laminated composites subjected to a tensile load was investigated by using the afore-mentioned model. The damage mechanism was analyzed and the strength was predicted for these materials. The experiments were done to verify the theoretical results. The results were consistent with those of the finite element numerical simulation. The validity of the modified numerical model is verified.
In order to optimize the designs and evaluate exactly the performances of PE/PE laminated composites, it is necessary to research the damage mechanisms of these materials, then to indicate the rules of the damage propagation, and to predict the effects on the various performances such as stiffness, strength and so on with the damage developing. A modified numerical model to simulate the mechanical behavior of PE/PE laminated composites was proposed based on the quasi-3-dimensional model concept. The damage propagation of three types of quasi-isotropic UHMWPE/HDPE laminated composites subjected to a tensile load was investigated by using the afore-mentioned model. The damage mechanism was analyzed and the strength was predicted for these materials. The experiments were done to verify the theoretical results. The results were consistent with those of the finite element numerical simulation. The validity of the modified numerical model is verified.
2005, 22(5): 147-154.
Abstract:
Based on the characteristics of the honeycomb sandwich composite material structures, the transient temperature field of the structures is assumed. Depending on this assumption and with the concern of the effect of temperature on the heat characteristic of the material, a method for honeycomb sandwich composite material structure heat transfer is obtained. It is an improved approach based on the 3-D anisotropy heat transfer theory and the composite material thermal laminated theory. The corresponding FEM equations are also constructed. An example solved with this method is given at the end. There are three different levels for nonlinear heat characteristics of the material discussed in this example. The results of the numerical example show that the nonlinear factors can be neglected only when the degree of the nonlinearity is very weak, and in most instances the nonlinear factors can not be neglected at all.
Based on the characteristics of the honeycomb sandwich composite material structures, the transient temperature field of the structures is assumed. Depending on this assumption and with the concern of the effect of temperature on the heat characteristic of the material, a method for honeycomb sandwich composite material structure heat transfer is obtained. It is an improved approach based on the 3-D anisotropy heat transfer theory and the composite material thermal laminated theory. The corresponding FEM equations are also constructed. An example solved with this method is given at the end. There are three different levels for nonlinear heat characteristics of the material discussed in this example. The results of the numerical example show that the nonlinear factors can be neglected only when the degree of the nonlinearity is very weak, and in most instances the nonlinear factors can not be neglected at all.
2005, 22(5): 155-161.
Abstract:
On the basis of available studies, a new model of representative volume elements of 3-D braided composites is proposed, which truly reflects the braided manner and coincides with the actual configuration of the braided composites. It can be used to predict the effective modulus of 3-D braided composites with Finite Element Method (FEM) and determine its stress field in reason. The finite element software was adopted to study the mechanical properties of this model, and the effective properties of elasticity were obtained. The results show that the ones of finite element calculation fit well with the experimental results and theoretical prediction, which demonstrates the validity of this model. In addition, based on the new model, the stress field of 3-D braided composites in tension or shearing is determined, which provides the basis for strength calculation in the future.
On the basis of available studies, a new model of representative volume elements of 3-D braided composites is proposed, which truly reflects the braided manner and coincides with the actual configuration of the braided composites. It can be used to predict the effective modulus of 3-D braided composites with Finite Element Method (FEM) and determine its stress field in reason. The finite element software was adopted to study the mechanical properties of this model, and the effective properties of elasticity were obtained. The results show that the ones of finite element calculation fit well with the experimental results and theoretical prediction, which demonstrates the validity of this model. In addition, based on the new model, the stress field of 3-D braided composites in tension or shearing is determined, which provides the basis for strength calculation in the future.
2005, 22(5): 162-171.
Abstract:
A sort of hexahedral microstructure unit-cell (MUC) geometric model is presented,whose performances are variable, aimed at resolving the troubles of the mechanical analysis about the gradient characteristics in the tubular and 3D braided composites components. The microstructure of MUC is diverse in multifarious 3D braided composites. Finding out the rules of the MUC geometric diversifications and the changed trends of its yarns volume fraction along with its coordinates,a feasible analysis model is provided for making certain the relationships among these factors and local mechanical performances in the MUC.A geometrical model was constituted for a kind of tubular 3D braided composites, of which the symmetrical axes are straight. The function relationships among the parameters were demonstrated in detail. The model about rectangular 3D braided composites preform is oversimplified. It might be used to describe the physical performances of spatial complicated and multi-dimensions braided composites and rebound to mechanical analysis for the composites.
A sort of hexahedral microstructure unit-cell (MUC) geometric model is presented,whose performances are variable, aimed at resolving the troubles of the mechanical analysis about the gradient characteristics in the tubular and 3D braided composites components. The microstructure of MUC is diverse in multifarious 3D braided composites. Finding out the rules of the MUC geometric diversifications and the changed trends of its yarns volume fraction along with its coordinates,a feasible analysis model is provided for making certain the relationships among these factors and local mechanical performances in the MUC.A geometrical model was constituted for a kind of tubular 3D braided composites, of which the symmetrical axes are straight. The function relationships among the parameters were demonstrated in detail. The model about rectangular 3D braided composites preform is oversimplified. It might be used to describe the physical performances of spatial complicated and multi-dimensions braided composites and rebound to mechanical analysis for the composites.
2005, 22(5): 172-177.
Abstract:
The dynamic character of the FGM rectangular plate was studied by the beam function combination method. The obtained analytical solutions of natural frequency and mode shape can be applied to 36 boundary conditions and arbitrary functional grades. A unified expression of natural frequencies for FGM rectangular plates under various boundary conditions was presented by further simplification. The given natural frequency and mode shape solutions are simple and practical for various engineering dynamic analyses of FGM plates.
The dynamic character of the FGM rectangular plate was studied by the beam function combination method. The obtained analytical solutions of natural frequency and mode shape can be applied to 36 boundary conditions and arbitrary functional grades. A unified expression of natural frequencies for FGM rectangular plates under various boundary conditions was presented by further simplification. The given natural frequency and mode shape solutions are simple and practical for various engineering dynamic analyses of FGM plates.
2005, 22(5): 178-183.
Abstract:
The time-temperature dependence of flexural strength of glass fiber reinforced plastics (GFRP,volume fraction of glass fiber:57%) laminates was studied by the accelerated testing method at high temperatures. The three-point bending tests were carried out at various temperatures and constant loading rates. The time-temperature dependence of GFRP laminates was investigated by means of the flexural strength master curve and time-temperature shift factor curve. The failure mechanisms at low temperature for short time to failure and at high temperature for long time to failure were investigated. With tensile delay fracture tests of the glass fiber, the time-temperature shift factors of flexural strength at various low temperatures for short time to failure were modified. The revised time-temperature shift factor curve of flexural strength of GFRP laminates agrees well with that of the dynamic Young’s modulus of the resin matrix. The flexural strength of GFRP laminates depends strongly on the viscoelasticity of the resin matrix.
The time-temperature dependence of flexural strength of glass fiber reinforced plastics (GFRP,volume fraction of glass fiber:57%) laminates was studied by the accelerated testing method at high temperatures. The three-point bending tests were carried out at various temperatures and constant loading rates. The time-temperature dependence of GFRP laminates was investigated by means of the flexural strength master curve and time-temperature shift factor curve. The failure mechanisms at low temperature for short time to failure and at high temperature for long time to failure were investigated. With tensile delay fracture tests of the glass fiber, the time-temperature shift factors of flexural strength at various low temperatures for short time to failure were modified. The revised time-temperature shift factor curve of flexural strength of GFRP laminates agrees well with that of the dynamic Young’s modulus of the resin matrix. The flexural strength of GFRP laminates depends strongly on the viscoelasticity of the resin matrix.
2005, 22(5): 184-189.
Abstract:
An analytical method for the longitudinal shear problem of magnetoelectroelastic composites with double periodically distributed cylindrical fibers is presented by means of the Eshelb y’ s effective inclusion method, combining the theory of doubly periodic and quasi-periodic analytical functions. The solution in series is obtained. And explicit expressions for the stress, electric displacement and magnetic induction are derived.The influences of microstructure of such heterogeneous materials on its magnetoelectroelastic properties were discussed by the numerical examples. The present method provides an efficient tool for analyzing the magnetoelectroelastic properties and designing microstructure of composite materials.
An analytical method for the longitudinal shear problem of magnetoelectroelastic composites with double periodically distributed cylindrical fibers is presented by means of the Eshelb y’ s effective inclusion method, combining the theory of doubly periodic and quasi-periodic analytical functions. The solution in series is obtained. And explicit expressions for the stress, electric displacement and magnetic induction are derived.The influences of microstructure of such heterogeneous materials on its magnetoelectroelastic properties were discussed by the numerical examples. The present method provides an efficient tool for analyzing the magnetoelectroelastic properties and designing microstructure of composite materials.
2005, 22(5): 190-196.
Abstract:
The compressive experiments and the corresponding finite element modeling were studied for the repaired composite laminates under compressive static load to evaluate the efficiency of repaired panels. The geometric non-linear and linear methods were applied to compute the stress-strain response of the repaired and the unrepaired laminates. The finite element models were analyzed with the three-dimensional S8R shell elements. The non-linear geometry effect was incorporated in the present analysis, and the user material subroutine (UMAT) was programmed to predict the damage initiation and its progression. The predicted strain distribution, damage evolution and strength of the laminates are verified with the experimental results.
The compressive experiments and the corresponding finite element modeling were studied for the repaired composite laminates under compressive static load to evaluate the efficiency of repaired panels. The geometric non-linear and linear methods were applied to compute the stress-strain response of the repaired and the unrepaired laminates. The finite element models were analyzed with the three-dimensional S8R shell elements. The non-linear geometry effect was incorporated in the present analysis, and the user material subroutine (UMAT) was programmed to predict the damage initiation and its progression. The predicted strain distribution, damage evolution and strength of the laminates are verified with the experimental results.
