2010 Vol. 27, No. 1
2010, 27(1): 1-6.
Abstract:
The chemorheological behavior of A40/DDM/DMTDA curing bisphenol-F epoxy resin for vacuum assisted resin transfer molding (VARTM) was studied by means of isothermal and dynamical viscosity experiments. A dual-Arrhenius viscosity model was established and used to simulate the rheological behavior of the epoxy resin system. The time-temperature equivalence of the system was also analysed with the reference temperature 100℃,and the shift factor aT was calculated by the dual-Arrhenius equation which was then used to predict the viscosity data at other temperatures. It was also used to modify the established viscosity model in order to deal with certain differences between the experiments and calculations for the resin with high viscosity. The viscosity values estimated from the modified model under isothermal and dynamic condition are in good agreement with the experimental ones. The dual-Arrhenius model can be used to predict the chemorheology of different processing parameters of VARTM process, which can be useful for optimization of composite manufacturing processes.
The chemorheological behavior of A40/DDM/DMTDA curing bisphenol-F epoxy resin for vacuum assisted resin transfer molding (VARTM) was studied by means of isothermal and dynamical viscosity experiments. A dual-Arrhenius viscosity model was established and used to simulate the rheological behavior of the epoxy resin system. The time-temperature equivalence of the system was also analysed with the reference temperature 100℃,and the shift factor aT was calculated by the dual-Arrhenius equation which was then used to predict the viscosity data at other temperatures. It was also used to modify the established viscosity model in order to deal with certain differences between the experiments and calculations for the resin with high viscosity. The viscosity values estimated from the modified model under isothermal and dynamic condition are in good agreement with the experimental ones. The dual-Arrhenius model can be used to predict the chemorheology of different processing parameters of VARTM process, which can be useful for optimization of composite manufacturing processes.
2010, 27(1): 7-11.
Abstract:
An ultrasonic technique was employed to in situ monitor the cure behavior of glass and carbon fiber reinforced vinyl-ester (VE) resins. The longitudinal sound velocities and at tenuations in the pure VE system, the glass fiber/VE composite system and the carbon fiber/VE system were investigated. The ultrasonic measurements show that the changes in the gel time, bulk storage modulus and activation energy of VE resins by the presence of the fiber fabrics can be observed. By comparison with the pure VE resins, the activation energy and cure reaction rate of the glass fiber/VE system become less (14 % cut down) and fast, respectively. However, the activation energy and cure reaction rate for the carbon fiber/VE system become large and slow. In sum, the ultrasonic technique as a non-invasive , in-situ and real time measurement technique can be used to study the curing behavior and processes of fiber reinforced composites.
An ultrasonic technique was employed to in situ monitor the cure behavior of glass and carbon fiber reinforced vinyl-ester (VE) resins. The longitudinal sound velocities and at tenuations in the pure VE system, the glass fiber/VE composite system and the carbon fiber/VE system were investigated. The ultrasonic measurements show that the changes in the gel time, bulk storage modulus and activation energy of VE resins by the presence of the fiber fabrics can be observed. By comparison with the pure VE resins, the activation energy and cure reaction rate of the glass fiber/VE system become less (14 % cut down) and fast, respectively. However, the activation energy and cure reaction rate for the carbon fiber/VE system become large and slow. In sum, the ultrasonic technique as a non-invasive , in-situ and real time measurement technique can be used to study the curing behavior and processes of fiber reinforced composites.
2010, 27(1): 12-17.
Abstract:
The solution mixing was used to fabricate a series of carboxylic multi-walled carbon nanotubes (CMWNTs ) /poly ( adipic acid- hexamethylene diamine ) (PA66 ) composites. The thermal and crystallizing properties of the composites were characterized by the thermogravimetric analysis (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarizering microscope ( POM). It is found that as the content of CMWNTs increases, the melting temperatures of the composites are almost unchanged, and the crystallinity and crystallizing temperature increase. CMWNTs act as a heterogeneous nucleation agent and do not affect the crystal form. POM analysis shows that addition of CMWNTs reduces the grain size of PA66. The interaction between CMWNTs and PA66 molecular chain is mainly Van Der Waals force and hydrogen bond. No evidence is given to prove the existence of chemical bonds between CMWNTs and PA66 molecular chains. The decomposition temperature of the composites rises slightly. The strong absorption of CMWNTs to the free radicals formed in the decomposition process decreases the rate of the composite decomposition.
The solution mixing was used to fabricate a series of carboxylic multi-walled carbon nanotubes (CMWNTs ) /poly ( adipic acid- hexamethylene diamine ) (PA66 ) composites. The thermal and crystallizing properties of the composites were characterized by the thermogravimetric analysis (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarizering microscope ( POM). It is found that as the content of CMWNTs increases, the melting temperatures of the composites are almost unchanged, and the crystallinity and crystallizing temperature increase. CMWNTs act as a heterogeneous nucleation agent and do not affect the crystal form. POM analysis shows that addition of CMWNTs reduces the grain size of PA66. The interaction between CMWNTs and PA66 molecular chain is mainly Van Der Waals force and hydrogen bond. No evidence is given to prove the existence of chemical bonds between CMWNTs and PA66 molecular chains. The decomposition temperature of the composites rises slightly. The strong absorption of CMWNTs to the free radicals formed in the decomposition process decreases the rate of the composite decomposition.
2010, 27(1): 18-24.
Abstract:
Two kinds of special tackifiers LSG-1 and LSG-2 were studied, which would be applied in resin transfer molding (RTM) technique to prepare 5284 resin composite. On the basis of analyzing the processing conditions and properties of the matrix resin, the ingredients of tackifers were preliminary determined. By testing the viscosity of the tackifier, 5284 resin and the compatibility between the tackifier and the matrix resin 5284 , the processing condition was determined. The springbacks of U-shaped bending and compression were combined with the microphotograph of the distributing condition of the tackifer to investigate the shape-fixing performance of the tackifier. The preform was fabricated by using the tackifier, and the influences of tackifiers on the processing properties and mechanical performance were studied by testing permeability of preforms and mechanical properties of the composite. The result s show that the tackifier has a satisfactory compatibility with the matrix resin, would not have any negative effect on the composite, and makes the preform have a favorable shape-fixing result .
Two kinds of special tackifiers LSG-1 and LSG-2 were studied, which would be applied in resin transfer molding (RTM) technique to prepare 5284 resin composite. On the basis of analyzing the processing conditions and properties of the matrix resin, the ingredients of tackifers were preliminary determined. By testing the viscosity of the tackifier, 5284 resin and the compatibility between the tackifier and the matrix resin 5284 , the processing condition was determined. The springbacks of U-shaped bending and compression were combined with the microphotograph of the distributing condition of the tackifer to investigate the shape-fixing performance of the tackifier. The preform was fabricated by using the tackifier, and the influences of tackifiers on the processing properties and mechanical performance were studied by testing permeability of preforms and mechanical properties of the composite. The result s show that the tackifier has a satisfactory compatibility with the matrix resin, would not have any negative effect on the composite, and makes the preform have a favorable shape-fixing result .
2010, 27(1): 25-31.
Abstract:
Based on the 2D plane strain finite element analysis model and strategy the influences of technology gap, curing cycle and residual stress on the performance of grid structure were studied. From numerical simulation of the co-curing process for a typical advanced grid stiffen structure, a method for appropriate technical gap is given, the strategy for reducing the gradient of coupling fields is provided and the mechanism of residual stress generation is explained. Therefore, this study will be meaningful for the proper determination of technical parameters during soft-mode aided co-curing processes.
Based on the 2D plane strain finite element analysis model and strategy the influences of technology gap, curing cycle and residual stress on the performance of grid structure were studied. From numerical simulation of the co-curing process for a typical advanced grid stiffen structure, a method for appropriate technical gap is given, the strategy for reducing the gradient of coupling fields is provided and the mechanism of residual stress generation is explained. Therefore, this study will be meaningful for the proper determination of technical parameters during soft-mode aided co-curing processes.
2010, 27(1): 32-36.
Abstract:
Methyl methacrylate-butadiene-styrene (MBS) core-shell copolymer was synthesized by grafting methyl methacrylate and styrene on SBR rubber particles using the seed emulsion polymerization. MBS/PVC blends were obtained by melt blending. The structure characteristics of MBS were analyzed, and the effects of different core-shell ratios in MBS on the disperse morphology, mechanical property and transparency property of MBS/PVC blends were investigated for obtaining high ductility and transparency MBS/PVC blends. With increasing the shell amount of MBS, dispersion states showed aggregation, network dispersion and homogeneous dispersion, the SBR brittle-ductile transition content for MBS/PVC blends decreases and the transparency of MBS/PVC blends decreases. The toughening mechanism of PVC blends with small MBS particles is shear yielding of the PVC matrix.
Methyl methacrylate-butadiene-styrene (MBS) core-shell copolymer was synthesized by grafting methyl methacrylate and styrene on SBR rubber particles using the seed emulsion polymerization. MBS/PVC blends were obtained by melt blending. The structure characteristics of MBS were analyzed, and the effects of different core-shell ratios in MBS on the disperse morphology, mechanical property and transparency property of MBS/PVC blends were investigated for obtaining high ductility and transparency MBS/PVC blends. With increasing the shell amount of MBS, dispersion states showed aggregation, network dispersion and homogeneous dispersion, the SBR brittle-ductile transition content for MBS/PVC blends decreases and the transparency of MBS/PVC blends decreases. The toughening mechanism of PVC blends with small MBS particles is shear yielding of the PVC matrix.
2010, 27(1): 37-42.
Abstract:
OMMT/ABS-polyamide-6 (PA6) (30/70, mass ratio) composites were prepared using PA6, ABS and
OMMT via the melt-mixing method. The morphology and mechanical properties of OMMT/ABS-PA6 composites
with various amounts of OMMT were investigated using scanning electron microscope (SEM), transmission electron microscope (TEM) and mechanical measurement. It was found that most of OMMT platelets were exclusively located within the PA6 phase. The particle size and distribution of ABS dispersed phase are gradually reduced with increasing the OMMT content. Moreover, the OMMT/ABS-PA6 composites have higher strength as compared to ABS-PA6 blends. Particularly, the flexural strength and flexural modulus of OMMT/ABS-PA6 composites increase to 94. 1 MPa and 3. 184 GPa respectively by adding the OMMT content to 7 wt%. At 3 wt% OMMT content, the notched impact strength of OMMT/ABS-PA6 composites obtains a maximal value 3. 7 kJ/m, and after tha , it tends to be unchanged.
OMMT/ABS-polyamide-6 (PA6) (30/70, mass ratio) composites were prepared using PA6, ABS and
OMMT via the melt-mixing method. The morphology and mechanical properties of OMMT/ABS-PA6 composites
with various amounts of OMMT were investigated using scanning electron microscope (SEM), transmission electron microscope (TEM) and mechanical measurement. It was found that most of OMMT platelets were exclusively located within the PA6 phase. The particle size and distribution of ABS dispersed phase are gradually reduced with increasing the OMMT content. Moreover, the OMMT/ABS-PA6 composites have higher strength as compared to ABS-PA6 blends. Particularly, the flexural strength and flexural modulus of OMMT/ABS-PA6 composites increase to 94. 1 MPa and 3. 184 GPa respectively by adding the OMMT content to 7 wt%. At 3 wt% OMMT content, the notched impact strength of OMMT/ABS-PA6 composites obtains a maximal value 3. 7 kJ/m, and after tha , it tends to be unchanged.
2010, 27(1): 43-50.
Abstract:
Na-modified Ca-montmorillonite (Ca-MMT ) was successfully prepared by a microwave-mechanochemistry technique. A new composite based on drug cetirizine hydrochloride (CTH) and Na-montmorillonite (Na-MMT) was prepared by the ion-exchange method, and the adsorption characteristics of CTH onto Na-MMT were evaluated. Through Fourier transformed infrared (FTIR) and X-ray diff raction (XRD) analyses, the st ructure of the resulted CTH/MMT composite was confirmed. The in vitro drug release research of the CTH/MMT composite in both artificial simulated gastric juice (ASGJ) and artificial simulated intestinal juice (ASIJ ) was used to study the efficiency, mechanism and kinetics of the drug release process. The results show that CTH intercalates in Na-MMT, and the interlayer spacing increases from 1. 25 nm to 2. 13 nm. The adsorption kinetics is found to follow the pseudo-second-order kinetic model. The adsorption equilibrium data corresponds to Freundlich model. In vitro experiment s show that CTH/MMT has a good sustained-release effect, and MMT can be used as a controlled-release carrier for CTH.
Na-modified Ca-montmorillonite (Ca-MMT ) was successfully prepared by a microwave-mechanochemistry technique. A new composite based on drug cetirizine hydrochloride (CTH) and Na-montmorillonite (Na-MMT) was prepared by the ion-exchange method, and the adsorption characteristics of CTH onto Na-MMT were evaluated. Through Fourier transformed infrared (FTIR) and X-ray diff raction (XRD) analyses, the st ructure of the resulted CTH/MMT composite was confirmed. The in vitro drug release research of the CTH/MMT composite in both artificial simulated gastric juice (ASGJ) and artificial simulated intestinal juice (ASIJ ) was used to study the efficiency, mechanism and kinetics of the drug release process. The results show that CTH intercalates in Na-MMT, and the interlayer spacing increases from 1. 25 nm to 2. 13 nm. The adsorption kinetics is found to follow the pseudo-second-order kinetic model. The adsorption equilibrium data corresponds to Freundlich model. In vitro experiment s show that CTH/MMT has a good sustained-release effect, and MMT can be used as a controlled-release carrier for CTH.
2010, 27(1): 51-56.
Abstract:
Al matrix composites withAl72Ni12Co16 particles of volume fraction ranging from 5 %～20 % were prepared. The quasicrystal material was obtained by casting Al72Ni12Co16 alloy on the water cooling copper subst rate. TEM and X-ray diffraction analysis indicate that the obtained material is single-phase quasicrystal material. Most defects of as-cast composites are eliminated by the hot extrusion, and the mechanical property test reveals that with addition ofAl72Ni12Co16, the tensile strength, yield strength and elastic modulus of Al matrix composites increase remarkably from 275 MPa, 200 MPa and 70 GPa to 410 MPa, 350 MPa and 102 GPa,respectively; on the other hand, the elongation decreases from 6 % to 3 %. Based on the above experiment, the fracture mechanism and strengthening mechanism were discussed in detail .
Al matrix composites withAl72Ni12Co16 particles of volume fraction ranging from 5 %～20 % were prepared. The quasicrystal material was obtained by casting Al72Ni12Co16 alloy on the water cooling copper subst rate. TEM and X-ray diffraction analysis indicate that the obtained material is single-phase quasicrystal material. Most defects of as-cast composites are eliminated by the hot extrusion, and the mechanical property test reveals that with addition ofAl72Ni12Co16, the tensile strength, yield strength and elastic modulus of Al matrix composites increase remarkably from 275 MPa, 200 MPa and 70 GPa to 410 MPa, 350 MPa and 102 GPa,respectively; on the other hand, the elongation decreases from 6 % to 3 %. Based on the above experiment, the fracture mechanism and strengthening mechanism were discussed in detail .
2010, 27(1): 57-61.
Abstract:
The high thermal conductivity SiCP/Al electronic packaging materials were successfully prepared by the spark plasma sintering (SPS) process. The effects of sintering temperature and holding time on the microstructure of SiCP/Al composites were researched. And thermo-physical characteristics of final composites were also evaluated. The results show that the thermal conductivity of 70 vol % SiCP/Al composites fabricated by SPS is 195. 5 W· (m·K)-1, which corresponds to that of 15 %W2Cu and decuples that of Kovar alloy; the density is 3. 0 g·cm-3; the thermal expansion coefficient (CTE) is 6. 8 ×10-6 K-1, which is close to the subst rate materials; and the bend st rength is 410 MPa, tensile strength is 190 MPa, satisfying the electronic packaging materials needs in thermal and mechanics properties.
The high thermal conductivity SiCP/Al electronic packaging materials were successfully prepared by the spark plasma sintering (SPS) process. The effects of sintering temperature and holding time on the microstructure of SiCP/Al composites were researched. And thermo-physical characteristics of final composites were also evaluated. The results show that the thermal conductivity of 70 vol % SiCP/Al composites fabricated by SPS is 195. 5 W· (m·K)-1, which corresponds to that of 15 %W2Cu and decuples that of Kovar alloy; the density is 3. 0 g·cm-3; the thermal expansion coefficient (CTE) is 6. 8 ×10-6 K-1, which is close to the subst rate materials; and the bend st rength is 410 MPa, tensile strength is 190 MPa, satisfying the electronic packaging materials needs in thermal and mechanics properties.
2010, 27(1): 62-67.
Abstract:
Dynamic compressive properties of a 40 vol %SiCP/2024Al composite and it s matrix 2024Al were studied at various strain rates using split Hopkinson pressure bar (SHPB). The flow stress of the composite and 2024Al is strain-rate insensitive above 1500 s-1, and the composite yield strength is higher than that of 2024Al. Different from the strain-hardening property of 2024Al, a st rain-softening performance is found in the compressive properties of the composite. Microstructure of the compressed composite specimens was characterized by SEM, some cavities, micro-cracks and particle fractures were observed in the specimens, and the matrix of the composite was softened, even melted by heat at higher strain rates. The strain-softening performance of the SiCP/2024Al composite at high strain rates is due to the inner damage and the heat softening. After being baked 3 h at 400℃ and self-cooling to the room temperature, the specimens of the composite and 2024Al were tested by SHPB. Compared to the original results, the mechanical properties of the matrix material are decreased significantly, but the property change of the composite is not obvious. The SiCP/2024Al composite presents a much better mechanical property stability withstanding high temperature than the matrix.
Dynamic compressive properties of a 40 vol %SiCP/2024Al composite and it s matrix 2024Al were studied at various strain rates using split Hopkinson pressure bar (SHPB). The flow stress of the composite and 2024Al is strain-rate insensitive above 1500 s-1, and the composite yield strength is higher than that of 2024Al. Different from the strain-hardening property of 2024Al, a st rain-softening performance is found in the compressive properties of the composite. Microstructure of the compressed composite specimens was characterized by SEM, some cavities, micro-cracks and particle fractures were observed in the specimens, and the matrix of the composite was softened, even melted by heat at higher strain rates. The strain-softening performance of the SiCP/2024Al composite at high strain rates is due to the inner damage and the heat softening. After being baked 3 h at 400℃ and self-cooling to the room temperature, the specimens of the composite and 2024Al were tested by SHPB. Compared to the original results, the mechanical properties of the matrix material are decreased significantly, but the property change of the composite is not obvious. The SiCP/2024Al composite presents a much better mechanical property stability withstanding high temperature than the matrix.
2010, 27(1): 68-72.
Abstract:
The 4. 4 %TiCP/7075 matrix composite was prepared by in-situ reactive near-liquidus casting. The sectioned specimens were heat-treated isothermally at 600℃ between the two-phase (liquid-solid) region (477～ 635℃) of the near-liquidus cast 7075 alloy for 10, 20, 40 and 60 min, then quenched in water. The grain size was measured using the software Image Pro Plus and the effect of in-situ TiCP on the reheating structure was analyzed. The result shows that the in-situ TiCP with fine and globular can not only keep near-liquidus cast 7075 alloy microstructure, but also cont rol evidently grains growth by pinning effect during reheating. Dealing under the same condition , the grain sizes of TiCP/7075 matrix composites are 30～40 μm less than those of 7075 alloy, which is very suitable for thixoforming.
The 4. 4 %TiCP/7075 matrix composite was prepared by in-situ reactive near-liquidus casting. The sectioned specimens were heat-treated isothermally at 600℃ between the two-phase (liquid-solid) region (477～ 635℃) of the near-liquidus cast 7075 alloy for 10, 20, 40 and 60 min, then quenched in water. The grain size was measured using the software Image Pro Plus and the effect of in-situ TiCP on the reheating structure was analyzed. The result shows that the in-situ TiCP with fine and globular can not only keep near-liquidus cast 7075 alloy microstructure, but also cont rol evidently grains growth by pinning effect during reheating. Dealing under the same condition , the grain sizes of TiCP/7075 matrix composites are 30～40 μm less than those of 7075 alloy, which is very suitable for thixoforming.
2010, 27(1): 73-78.
Abstract:
For get ting better properties and simplifying the process, the Cf/Cucomposites were prepared by one-step hot-pressing sintering. The mechanism of the interface reaction between Cu and carbon fiber (Cf) and the microstructure of Cf/Cu composites were studied. The effects of different Ti contents on the density, hardness and bending strength of Cf/Cu composites were investigated. The results indicate that TiC layer surrounding Cf is generated in the ternary system of Cu2C2Ti and the TiC layer decreases the wetting angle between the liquid Cu and the solid Cf, which improves the combination between Cu and Cf. The mechanism of formation of TiC layer was discussed and a microstructure model of the reaction between Ti dissolved in the liquid Cu and C was brought forward. The formation of TiC layer is good for increasing the properties of the composites. When the mass fraction of Ti is 16. 7 %, the synthetic properties of the composites are the best in this system with Shore hardness HS66.94 and flexural strength 97. 59 MPa.
For get ting better properties and simplifying the process, the Cf/Cucomposites were prepared by one-step hot-pressing sintering. The mechanism of the interface reaction between Cu and carbon fiber (Cf) and the microstructure of Cf/Cu composites were studied. The effects of different Ti contents on the density, hardness and bending strength of Cf/Cu composites were investigated. The results indicate that TiC layer surrounding Cf is generated in the ternary system of Cu2C2Ti and the TiC layer decreases the wetting angle between the liquid Cu and the solid Cf, which improves the combination between Cu and Cf. The mechanism of formation of TiC layer was discussed and a microstructure model of the reaction between Ti dissolved in the liquid Cu and C was brought forward. The formation of TiC layer is good for increasing the properties of the composites. When the mass fraction of Ti is 16. 7 %, the synthetic properties of the composites are the best in this system with Shore hardness HS66.94 and flexural strength 97. 59 MPa.
2010, 27(1): 79-85.
Abstract:
Copper mat rix composites were prepared through powder metallurgic technique. The relationship between speed and pressure of friction and the friction and wear properties of the materials were studied on a pin-on-disk tester in the pressure range of 0. 5～1. 2 MPa under dry and wet conditions. The results demonstrate that thmajor factors affecting the performance are the nature of loading and the state of third bodies. For dry fiction, whe the speed is low, the f riction force is close to static. Such loading allows the third bodies to stay in a porous state increases the level of engagement of asperity, and results in a higher friction coefficient. As the third bodie compact, they provide more lubricating effect, which attenuates the mechanical clenching of asperity, and lowers the friction coefficient as well as wear of the materials. At high speed, hard particulates on the friction surfaces are more likely to be smashed due to impacts among the micro-rises. The broken hard particulates disperse and harden the friction surfaces, causing an increase in the friction coefficient. The friction pressure affects the high speed friction properties significantly because the heavy loading intensifies the deformation and damage of the friction surfaces. Under wet conditions, the effects of flow and lubrication of the water film in lowering the friction coefficient and reducing the wear rate are apparent only at low speed and low pressure. At high speed and high pressure evaporation at elevated temperature and centrifugal action break the water film and consequently the friction and wear properties of the friction materials are similar to those of dry friction.
Copper mat rix composites were prepared through powder metallurgic technique. The relationship between speed and pressure of friction and the friction and wear properties of the materials were studied on a pin-on-disk tester in the pressure range of 0. 5～1. 2 MPa under dry and wet conditions. The results demonstrate that thmajor factors affecting the performance are the nature of loading and the state of third bodies. For dry fiction, whe the speed is low, the f riction force is close to static. Such loading allows the third bodies to stay in a porous state increases the level of engagement of asperity, and results in a higher friction coefficient. As the third bodie compact, they provide more lubricating effect, which attenuates the mechanical clenching of asperity, and lowers the friction coefficient as well as wear of the materials. At high speed, hard particulates on the friction surfaces are more likely to be smashed due to impacts among the micro-rises. The broken hard particulates disperse and harden the friction surfaces, causing an increase in the friction coefficient. The friction pressure affects the high speed friction properties significantly because the heavy loading intensifies the deformation and damage of the friction surfaces. Under wet conditions, the effects of flow and lubrication of the water film in lowering the friction coefficient and reducing the wear rate are apparent only at low speed and low pressure. At high speed and high pressure evaporation at elevated temperature and centrifugal action break the water film and consequently the friction and wear properties of the friction materials are similar to those of dry friction.
2010, 27(1): 86-90.
Abstract:
The semi-solid Al2O3P/Al-Cualloys cast with in-situ near-liquidus casting technology were reheated, and its microstructural evolution and grain growth mechanism were studied by means of optical microscope. The grain sizes and the volume fraction of liquid were measured using Image Pro Plus , and compared with theoretical calculation. The result s indicate that under the combination of reheating temperature 590℃and holding time 10～60 min, with no Al2O3 particles the Al-6. 8 %Cu mat rix alloy has average grain size of 89～132 μm and liquid volume f raction 14 %～26. 8 %, while 3. 6 wt%Al2O3P/Al-6. 8 %Cu composite has average grain size of 73～107 μm and liquid volume fraction of 11. 6 %～ 20. 9 %. The in-situ Al2O3 particle can control the grain sizes and the volume fraction of liquid growth evidently during reheating. Thus, the conclusion will offer one kind of new mentality for optimizing semi-solid microstructure.
The semi-solid Al2O3P/Al-Cualloys cast with in-situ near-liquidus casting technology were reheated, and its microstructural evolution and grain growth mechanism were studied by means of optical microscope. The grain sizes and the volume fraction of liquid were measured using Image Pro Plus , and compared with theoretical calculation. The result s indicate that under the combination of reheating temperature 590℃and holding time 10～60 min, with no Al2O3 particles the Al-6. 8 %Cu mat rix alloy has average grain size of 89～132 μm and liquid volume f raction 14 %～26. 8 %, while 3. 6 wt%Al2O3P/Al-6. 8 %Cu composite has average grain size of 73～107 μm and liquid volume fraction of 11. 6 %～ 20. 9 %. The in-situ Al2O3 particle can control the grain sizes and the volume fraction of liquid growth evidently during reheating. Thus, the conclusion will offer one kind of new mentality for optimizing semi-solid microstructure.
2010, 27(1): 91-97.
Abstract:
Fe78Si9B13/Ni laminated composite was prepared in the form of three-ply (Ni-Fe78Si9B13-Ni) laminated structure by the pulse electrodeposition method. The microst ructures of the laminated composite were investigated by SEM and TEM. The average grain size of Ni layers is about 50 nm. The laminated composite has a good interfacial bonding between amorphous layer and nano-Ni layers. The laminated composite possesses a very high tensile strength (2090 MPa) and reasonable tensile elongation (8. 5 %) at room temperature , which is much larger than that of monolithic amorphous Fe78Si9B13ribbon (1. 39 %). The elongation of 115. 5 % was obtained at 450℃, which is greatly higher than that of such amorphous ribbon (36. 3 %). The aim of enhancing the plasticity of amorphous ribbon by producing laminated composite is achieved.
Fe78Si9B13/Ni laminated composite was prepared in the form of three-ply (Ni-Fe78Si9B13-Ni) laminated structure by the pulse electrodeposition method. The microst ructures of the laminated composite were investigated by SEM and TEM. The average grain size of Ni layers is about 50 nm. The laminated composite has a good interfacial bonding between amorphous layer and nano-Ni layers. The laminated composite possesses a very high tensile strength (2090 MPa) and reasonable tensile elongation (8. 5 %) at room temperature , which is much larger than that of monolithic amorphous Fe78Si9B13ribbon (1. 39 %). The elongation of 115. 5 % was obtained at 450℃, which is greatly higher than that of such amorphous ribbon (36. 3 %). The aim of enhancing the plasticity of amorphous ribbon by producing laminated composite is achieved.
2010, 27(1): 98-103.
Abstract:
To investigate the thermal shock resistance of 3D C/SiC composites with a thin interlayer under stresses and oxidizing atmospheres whose thickness of the interlayer is thinner than the standard one (200 nm), the thermal shock tests were carried out in the temperature range between 700 and 1200℃ in oxidizing atmospheres under fatigue or creep stresses. Effects of stress and atmosphere on the degradation behaviors of the 3D C/SiC composite were investigated by the residual tensile strength , the stress-displacement curves, the length change curves and the morphologies. It is found that the oxidation of carbon and the degradation saturation of the composite under thermal shock are accelerated by the stress because of the cracks widen. The effect of creep stress on the degradation of the composite is greater than that of the fatigue stress. The residual tensile strength of the composite is enhanced by alimited oxidation and debonding of the interlayer resulted from the oxidizing atmosphere and the stress. It is shown that the thermal shock resistance of the composite with a thin interlayer is good even under the stress
To investigate the thermal shock resistance of 3D C/SiC composites with a thin interlayer under stresses and oxidizing atmospheres whose thickness of the interlayer is thinner than the standard one (200 nm), the thermal shock tests were carried out in the temperature range between 700 and 1200℃ in oxidizing atmospheres under fatigue or creep stresses. Effects of stress and atmosphere on the degradation behaviors of the 3D C/SiC composite were investigated by the residual tensile strength , the stress-displacement curves, the length change curves and the morphologies. It is found that the oxidation of carbon and the degradation saturation of the composite under thermal shock are accelerated by the stress because of the cracks widen. The effect of creep stress on the degradation of the composite is greater than that of the fatigue stress. The residual tensile strength of the composite is enhanced by alimited oxidation and debonding of the interlayer resulted from the oxidizing atmosphere and the stress. It is shown that the thermal shock resistance of the composite with a thin interlayer is good even under the stress
2010, 27(1): 104-108.
Abstract:
The high temperature inoxidizable behavior of SiC/MoSi2 and SiC/Mo (Si, Al)2 prepared by the infilt ration method was studied, and the shape and mass increase induced by oxidate process were discussed in the paper. The results show that the composites will be inactive after high temperature oxidation for 3 h, and the“Pest” phenomenon will disappear when the composites continue to oxide at 500℃. The oxide mass gain of SiC/Mo(Si, Al)2 is bigger than that of SiC/MoSi2. When SiC reinforcement is in-situ formed in SiC/MoSi2 composite, the ability of inoxidation is bet ter because of the higher interface binding force.
The high temperature inoxidizable behavior of SiC/MoSi2 and SiC/Mo (Si, Al)2 prepared by the infilt ration method was studied, and the shape and mass increase induced by oxidate process were discussed in the paper. The results show that the composites will be inactive after high temperature oxidation for 3 h, and the“Pest” phenomenon will disappear when the composites continue to oxide at 500℃. The oxide mass gain of SiC/Mo(Si, Al)2 is bigger than that of SiC/MoSi2. When SiC reinforcement is in-situ formed in SiC/MoSi2 composite, the ability of inoxidation is bet ter because of the higher interface binding force.
2010, 27(1): 109-117.
Abstract:
TiB2-TiC eutectic composite ceramics were prepared by combustion synthesis under high gravity. XRD ,SEM and EDS results show that TiB2-TiC composites are mainly composed of the eutectic microst ructures of TiC matrix, in which a large number of the fine TiB2 platelet grains are dispersed uniformly ; meanwhile, at the boundaries of the eutectic microst ructures there discontinuously disperse the ε-carbides with the enrichment of Tiatoms, and a few of isolated , irregular α-Al2O3 grains and Al2O3-ZrO2 colonies are also observed. Because high-temperature chemical reaction results in the full-liquid products, and the introduction of high gravity induces the Stocks flow in the melts, leading to the formation of layered melt s consisting of liquid Ti-Cr-C-B and liquid oxides, it is considered that TiB2-TiC composites grow through eutectic t ransformation far away f rom the equilibrium state.The results of properties indicate that with increasing mass fraction of B4C + Ti + C in combustion systems , the relative density and f racture toughness of TiB2-TiC composites are all among 97 %～99 % and 6. 5 ～7. 1 MPa·m1/2 , respectively, and the Vickers hardness and flexural strength are increased gradually to the maximum values of 28. 6 GPa and 615 MPa, respectively.
TiB2-TiC eutectic composite ceramics were prepared by combustion synthesis under high gravity. XRD ,SEM and EDS results show that TiB2-TiC composites are mainly composed of the eutectic microst ructures of TiC matrix, in which a large number of the fine TiB2 platelet grains are dispersed uniformly ; meanwhile, at the boundaries of the eutectic microst ructures there discontinuously disperse the ε-carbides with the enrichment of Tiatoms, and a few of isolated , irregular α-Al2O3 grains and Al2O3-ZrO2 colonies are also observed. Because high-temperature chemical reaction results in the full-liquid products, and the introduction of high gravity induces the Stocks flow in the melts, leading to the formation of layered melt s consisting of liquid Ti-Cr-C-B and liquid oxides, it is considered that TiB2-TiC composites grow through eutectic t ransformation far away f rom the equilibrium state.The results of properties indicate that with increasing mass fraction of B4C + Ti + C in combustion systems , the relative density and f racture toughness of TiB2-TiC composites are all among 97 %～99 % and 6. 5 ～7. 1 MPa·m1/2 , respectively, and the Vickers hardness and flexural strength are increased gradually to the maximum values of 28. 6 GPa and 615 MPa, respectively.
2010, 27(1): 118-122.
Abstract:
Aluminium nitride-molybdenum ceramics with Y2O3 additive were prepared via hot-pressing in N2 atmosphere at 1800～1900℃. The phase constitution and microstructure were detected by XRD and SEM. The electrical resistivity and microwave attenuation property were characterized by the four point valves technique and microstrip line method. The results show that, in the 2～20 GHz frequency region, when the content of Mo is between 4. 56 vol %～15. 03 vol %, the composites present wide-band at tenuation and with the increase of Mo content and sintering temperature , the at tenuation increases ; when Mo content is between 16. 18 vol %～24. 88 vol %, the materials show narrow-band at tenuation under 6, 10, 14, 18 GHz. According to the percolation model, the fitting curve of electrical resistivity indicates that the percolation threshold Vc of Mo is 14. 87 vol % and the corresponding resistivity of the composite is 11. 59 Ω·m. The attenuation characteristic transfers from wide-band to narrow-band as the volume fraction of Mo is above Vc.
Aluminium nitride-molybdenum ceramics with Y2O3 additive were prepared via hot-pressing in N2 atmosphere at 1800～1900℃. The phase constitution and microstructure were detected by XRD and SEM. The electrical resistivity and microwave attenuation property were characterized by the four point valves technique and microstrip line method. The results show that, in the 2～20 GHz frequency region, when the content of Mo is between 4. 56 vol %～15. 03 vol %, the composites present wide-band at tenuation and with the increase of Mo content and sintering temperature , the at tenuation increases ; when Mo content is between 16. 18 vol %～24. 88 vol %, the materials show narrow-band at tenuation under 6, 10, 14, 18 GHz. According to the percolation model, the fitting curve of electrical resistivity indicates that the percolation threshold Vc of Mo is 14. 87 vol % and the corresponding resistivity of the composite is 11. 59 Ω·m. The attenuation characteristic transfers from wide-band to narrow-band as the volume fraction of Mo is above Vc.
2010, 27(1): 123-128.
Abstract:
A mechanical multi-rollers system was used to spread large tow carbon fibers, the force condition of large tow carbon fibers on different shaped rollers and the possible movement of fibers were analyzed, and the damage level and the dist ribution of spreaded fibers spreaded by different shaped rollers were studied also. Af ter amulti-rollers system within several equal diameter special-shaped rollers as kernel parts was determined , what kind of roles those factors such as the curvature of the special-shaped rollers and the tension play in spreading large tow carbon fibers were studied. It is determined that the optimal curvature radius of the special-shaped rollers and optimal tension exerted on fibers are 330 mm and 46. 6 N respectively.
A mechanical multi-rollers system was used to spread large tow carbon fibers, the force condition of large tow carbon fibers on different shaped rollers and the possible movement of fibers were analyzed, and the damage level and the dist ribution of spreaded fibers spreaded by different shaped rollers were studied also. Af ter amulti-rollers system within several equal diameter special-shaped rollers as kernel parts was determined , what kind of roles those factors such as the curvature of the special-shaped rollers and the tension play in spreading large tow carbon fibers were studied. It is determined that the optimal curvature radius of the special-shaped rollers and optimal tension exerted on fibers are 330 mm and 46. 6 N respectively.
2010, 27(1): 129-132.
Abstract:
The relationship between the microstructure and the interfacial properties of C/C composite was researched in this paper. The microstructure features of the interfacial layers in C/C composite obtained by high resolution Micro-CT were statistically analyzed , and the probability density function of the interfacial microstructure was achieved. Mechanical properties of the interfacial layers in C/C composite were calculated by a hypothetic analysis model. The distribution of mechanical properties can be obtained through introducing a probability density function of the interfacial microstructure into this analysis model. The mechanical properties of the interfacial layers in C/C composite were measured by the push out tests of fiber bundles. Comparing the calculation results with the experimental results, it is found that the means and dispersions of these two results are accordant.
The relationship between the microstructure and the interfacial properties of C/C composite was researched in this paper. The microstructure features of the interfacial layers in C/C composite obtained by high resolution Micro-CT were statistically analyzed , and the probability density function of the interfacial microstructure was achieved. Mechanical properties of the interfacial layers in C/C composite were calculated by a hypothetic analysis model. The distribution of mechanical properties can be obtained through introducing a probability density function of the interfacial microstructure into this analysis model. The mechanical properties of the interfacial layers in C/C composite were measured by the push out tests of fiber bundles. Comparing the calculation results with the experimental results, it is found that the means and dispersions of these two results are accordant.
2010, 27(1): 133-138.
Abstract:
A new fabrication technology of carbon fiber reinforced pyramidal lattice truss core sandwich structures was presented. It dealt with the disadvantage of such traditional technology as the facesheets and core needing bonded or joined additionally. Both ends of truss members were embedded into the facesheets without evident interface between the core and facesheets. The pyramidal lattice truss core sandwich structures were tested under compressive load. Observation of the buckling and splitting of truss members was done during the tests. And the compressive stiffness and the limit buckling load of the lattice truss core sandwich structures were calculated theoretically. Compared with the traditional sandwich structures, the pyramidal lattice truss core sandwich structures have the advantages of lower density, higher specific stiffness and higher specific strength.
A new fabrication technology of carbon fiber reinforced pyramidal lattice truss core sandwich structures was presented. It dealt with the disadvantage of such traditional technology as the facesheets and core needing bonded or joined additionally. Both ends of truss members were embedded into the facesheets without evident interface between the core and facesheets. The pyramidal lattice truss core sandwich structures were tested under compressive load. Observation of the buckling and splitting of truss members was done during the tests. And the compressive stiffness and the limit buckling load of the lattice truss core sandwich structures were calculated theoretically. Compared with the traditional sandwich structures, the pyramidal lattice truss core sandwich structures have the advantages of lower density, higher specific stiffness and higher specific strength.
2010, 27(1): 139-143.
Abstract:
Fe81-xCoxZr7Nb2B10(x = 2, 4, 6) amorphous alloys were prepared by single roller melt-spinning and annealed at different temperatures. The crystalline processes and magnetic properties of the alloys were studied by X-ray diff raction and vibrating sample magnetometer. The results show that when quenching speed reaches 30 m/s, Fe81-xCoxZr7Nb2B10(x = 2, 4, 6) amorphous alloys are formed. The crystalline process of Fe79Co2Zr7Nb2B10 is amorphous→amorphous +α-Fe→α-Fe + Fe3Zr + Fe2Nb0.4Zr0.6. The crystalline process of Fe77Co4Zr7Nb2B10 is the same as Fe75Co6Zr7Nb2B10: amorphous→amorphous +α-Fe→α-Fe + Fe3Zr→α-Fe + Fe3Zr + Fe2Nb0.4Zr0.6.Increasing Co content restrains the nucleation of α-Fe and makes Fe3Zr precipitate easy after annealing. The changing trends of magnetic properties of Fe81-xCoxZr7Nb2B10(x = 2, 4, 6) alloys are the same with increasing annealing temperature. Annealed below 530℃, special saturation magnetization (Ms) changes a little. After 530℃, Ms increases sharply. Annealed at 530℃, coercivity (Hc) reaches the minimum. After 530℃, Hc increases with increasing the annealing temperature.
Fe81-xCoxZr7Nb2B10(x = 2, 4, 6) amorphous alloys were prepared by single roller melt-spinning and annealed at different temperatures. The crystalline processes and magnetic properties of the alloys were studied by X-ray diff raction and vibrating sample magnetometer. The results show that when quenching speed reaches 30 m/s, Fe81-xCoxZr7Nb2B10(x = 2, 4, 6) amorphous alloys are formed. The crystalline process of Fe79Co2Zr7Nb2B10 is amorphous→amorphous +α-Fe→α-Fe + Fe3Zr + Fe2Nb0.4Zr0.6. The crystalline process of Fe77Co4Zr7Nb2B10 is the same as Fe75Co6Zr7Nb2B10: amorphous→amorphous +α-Fe→α-Fe + Fe3Zr→α-Fe + Fe3Zr + Fe2Nb0.4Zr0.6.Increasing Co content restrains the nucleation of α-Fe and makes Fe3Zr precipitate easy after annealing. The changing trends of magnetic properties of Fe81-xCoxZr7Nb2B10(x = 2, 4, 6) alloys are the same with increasing annealing temperature. Annealed below 530℃, special saturation magnetization (Ms) changes a little. After 530℃, Ms increases sharply. Annealed at 530℃, coercivity (Hc) reaches the minimum. After 530℃, Hc increases with increasing the annealing temperature.
2010, 27(1): 144-149.
Abstract:
In order to solve the coarsening problem of reinforcing particles in fabrication of traditional composite solders and enhance the properties of lead-free composite solders, the eutectic Sn-3.5Ag and Sn-3.0Ag-0.5Cu were selected as solder matrix, and three different nano-sized polyhedral oligomeric silsesquioxane(POSS) particulates were used as reinforcing particles to form composite solders. The spreadability properties, mechanical performance, and creep rupture lives of solder matrix and their new composite solders with different mass fractions were studied. The experimental results indicate that the new composite solders and their joints show better wettability, mechanical properties, as well as longer creep rupture lives than those of the solder matrix. Besides, Sn-Ag-Cu composite solder joints exhibit better properties compared with Sn-Ag composite solder joints.
In order to solve the coarsening problem of reinforcing particles in fabrication of traditional composite solders and enhance the properties of lead-free composite solders, the eutectic Sn-3.5Ag and Sn-3.0Ag-0.5Cu were selected as solder matrix, and three different nano-sized polyhedral oligomeric silsesquioxane(POSS) particulates were used as reinforcing particles to form composite solders. The spreadability properties, mechanical performance, and creep rupture lives of solder matrix and their new composite solders with different mass fractions were studied. The experimental results indicate that the new composite solders and their joints show better wettability, mechanical properties, as well as longer creep rupture lives than those of the solder matrix. Besides, Sn-Ag-Cu composite solder joints exhibit better properties compared with Sn-Ag composite solder joints.
2010, 27(1): 150-154.
Abstract:
Experiments were carried out to test the alkaline resistance properties of basalt fibers and their effects on the mechanical property of fiber reinforced concrete. Mass loss rates of fibers were weighed after being soaked at different aqueous alkali and at different temperatures respectively. Meanwhile, mechanical properties of basalt fiber reinforced concrete (BFRC) were tested with three different volume fractions of basalt fiber. Microphotographs of corroded fibers show that as alkalinity and curing temperature increase, the scaling of fiber appeares even worse. However, mechanical properties of BFRC at the early age are close to those of the reference while compressive strength and flexural strength of BFRC at 28 d are deeply lower than those of the reference. Microstructure images of basalt fiber in concrete appeare to be corroded seriously. The results show that instability of basalt fiber in alkaline solution may impact the mechanical property of BFRC.
Experiments were carried out to test the alkaline resistance properties of basalt fibers and their effects on the mechanical property of fiber reinforced concrete. Mass loss rates of fibers were weighed after being soaked at different aqueous alkali and at different temperatures respectively. Meanwhile, mechanical properties of basalt fiber reinforced concrete (BFRC) were tested with three different volume fractions of basalt fiber. Microphotographs of corroded fibers show that as alkalinity and curing temperature increase, the scaling of fiber appeares even worse. However, mechanical properties of BFRC at the early age are close to those of the reference while compressive strength and flexural strength of BFRC at 28 d are deeply lower than those of the reference. Microstructure images of basalt fiber in concrete appeare to be corroded seriously. The results show that instability of basalt fiber in alkaline solution may impact the mechanical property of BFRC.
2010, 27(1): 155-161.
Abstract:
The interfacial fatigue damage behaviors of two reinforced concrete (RC) beams strengthened with fiber reinforced plastic (FRP) were recorded with the infrared detecting method, and based on a series of fatigue tests the interfacial fatigue properties and interfacial fatigue lives were studied. It is found that the infrared detecting method can be used to monitor the interfacial debonding effectively because the difference in infrared temperature between the bonding and debonding areas is obvious. The interfacial debonding initiates at the concrete cracks around the mid-span and then expands to one end of the beam, in which the process for the initiation and stable or unstable growth of the interfacial debonding has been observed with the stable phase about 99 % of the total interfacial fatigue life. In the main fatigue phase, the interfacial damage is little and increases slowly; in addition FRP stress changes smoothly, showing that the interfacial fatigue properties are stable. The use of FRP high strength is restrained by the interfacial fatigue failure, and at last according to test data a prediction approach for interfacial lives is given.
The interfacial fatigue damage behaviors of two reinforced concrete (RC) beams strengthened with fiber reinforced plastic (FRP) were recorded with the infrared detecting method, and based on a series of fatigue tests the interfacial fatigue properties and interfacial fatigue lives were studied. It is found that the infrared detecting method can be used to monitor the interfacial debonding effectively because the difference in infrared temperature between the bonding and debonding areas is obvious. The interfacial debonding initiates at the concrete cracks around the mid-span and then expands to one end of the beam, in which the process for the initiation and stable or unstable growth of the interfacial debonding has been observed with the stable phase about 99 % of the total interfacial fatigue life. In the main fatigue phase, the interfacial damage is little and increases slowly; in addition FRP stress changes smoothly, showing that the interfacial fatigue properties are stable. The use of FRP high strength is restrained by the interfacial fatigue failure, and at last according to test data a prediction approach for interfacial lives is given.
2010, 27(1): 162-166.
Abstract:
By introducing proper Westergaard stress function, the stress fields for modeⅠand Ⅱproblems of periodic cracks in orthotropic composites were analyzed using the complex variable function method and approach of undetermined coefficients. Firstly, the stress intensity factors (SIFs) at the crack tip for modeⅠand Ⅱproblems were presented under symmetrical loadings and skew-symmetrical loadings at infinity. The analytic expressions of the stress fields are then induced by the SIFs. In addition, the stress fields are related to the material constants, which is the characteristic of orthotropic materials different from the isotropic materials. Due to the distribution of periodic cracks in an orthotropic plate, the SIFs are determined by the shape factor. The results show that the shape factor increases as the crack length becomes longer, but decreases as the crack spacing becomes larger. Especially, the present result can reduce to the case of the central crack in an orthotropic plate when the crack spacing tends to infinity.
By introducing proper Westergaard stress function, the stress fields for modeⅠand Ⅱproblems of periodic cracks in orthotropic composites were analyzed using the complex variable function method and approach of undetermined coefficients. Firstly, the stress intensity factors (SIFs) at the crack tip for modeⅠand Ⅱproblems were presented under symmetrical loadings and skew-symmetrical loadings at infinity. The analytic expressions of the stress fields are then induced by the SIFs. In addition, the stress fields are related to the material constants, which is the characteristic of orthotropic materials different from the isotropic materials. Due to the distribution of periodic cracks in an orthotropic plate, the SIFs are determined by the shape factor. The results show that the shape factor increases as the crack length becomes longer, but decreases as the crack spacing becomes larger. Especially, the present result can reduce to the case of the central crack in an orthotropic plate when the crack spacing tends to infinity.
2010, 27(1): 167-172.
Abstract:
A dual two-scale method was presented for computing 3D st ress fields of unidirectional-fibre reinforced composites considering the interphase. In the prediction of properties, the homogenized inclusion was obtained by homogenizing the fibre and the interphase, and the macroscopic homogenized material was obtained by homogenizing the homogenized inclusion and the matrix. In the characterization of 3D stress fields, by twice stress transmissions, the stress fields of the unit cell and the stress concent ration area were obtained in turn by the two-scale asymptotic technique. Combining with the finite element method, the 3D stress fields of the proposed composites, which are under the macroscopic axial uniform tensile load, were computed by the dual two-cale method. The numerical results show that the maximum stress occurs within the region which is in the middle section of each fibre and close to the border between fibre and interphase. The influence of different interphases on the distributions of stress fields was also discussed. The results show that arithmetical transition of the properties of fibre, interphase and matrix is beneficial to releasing stress concent ration.
A dual two-scale method was presented for computing 3D st ress fields of unidirectional-fibre reinforced composites considering the interphase. In the prediction of properties, the homogenized inclusion was obtained by homogenizing the fibre and the interphase, and the macroscopic homogenized material was obtained by homogenizing the homogenized inclusion and the matrix. In the characterization of 3D stress fields, by twice stress transmissions, the stress fields of the unit cell and the stress concent ration area were obtained in turn by the two-scale asymptotic technique. Combining with the finite element method, the 3D stress fields of the proposed composites, which are under the macroscopic axial uniform tensile load, were computed by the dual two-cale method. The numerical results show that the maximum stress occurs within the region which is in the middle section of each fibre and close to the border between fibre and interphase. The influence of different interphases on the distributions of stress fields was also discussed. The results show that arithmetical transition of the properties of fibre, interphase and matrix is beneficial to releasing stress concent ration.
2010, 27(1): 173-178.
Abstract:
The multidirectional(MD) composite laminates subjected to in-plane loading are in the three dimensional stress state due to the presence of interlaminar stresses. A quasi-3D finite element model consisting of plate elements, spring elements and rigid elements was established which, together with the fatigue damage models of unidirectional laminate, is used to construct a fatigue life estimation procedure for MD laminates with arbitrary stacking sequences. This is an integration of stress analysis, static strength analysis, cumulative damage analysis and the material property degradations. The application of the procedure for two T300/QY8911 composite laminates demonst ates good agreement of fatigue life prediction with the experiments.
The multidirectional(MD) composite laminates subjected to in-plane loading are in the three dimensional stress state due to the presence of interlaminar stresses. A quasi-3D finite element model consisting of plate elements, spring elements and rigid elements was established which, together with the fatigue damage models of unidirectional laminate, is used to construct a fatigue life estimation procedure for MD laminates with arbitrary stacking sequences. This is an integration of stress analysis, static strength analysis, cumulative damage analysis and the material property degradations. The application of the procedure for two T300/QY8911 composite laminates demonst ates good agreement of fatigue life prediction with the experiments.
2010, 27(1): 179-184.
Abstract:
The filament-process int roduces the fiber undulations and the nonorthogonality of the crossover geometry into thin-shell cylinders. This research identified the micromechanical geometry in the fiber crosserover regions of filament-wound cylinders. A new method for calculating the stiffness of filament winding composites is presented. The calculating process is roughly divided into three steps. First, the 3D stiffness for the undulating layer was converted to a 2D effective stiffness through the two angles, namely the angle of inclination, the out-of-plane angle due to the fiber undulation, and the filament winding angle , the in-plane angle. Next, lamination theory was used to obtain the local laminate stiffness which was functions of the undlation direction, and the stiffness constants were numerically integrated and averaged along the length of the undulation. Third, the whole stiffness of filament winding composites was calculated through the transformed matrix between the principal coordinate axis and the direction of filament-winding. Some important changes exhibited by the stiffness matrices, especially the stiffness coupling effects due to the fiber undulation are obvious.
The filament-process int roduces the fiber undulations and the nonorthogonality of the crossover geometry into thin-shell cylinders. This research identified the micromechanical geometry in the fiber crosserover regions of filament-wound cylinders. A new method for calculating the stiffness of filament winding composites is presented. The calculating process is roughly divided into three steps. First, the 3D stiffness for the undulating layer was converted to a 2D effective stiffness through the two angles, namely the angle of inclination, the out-of-plane angle due to the fiber undulation, and the filament winding angle , the in-plane angle. Next, lamination theory was used to obtain the local laminate stiffness which was functions of the undlation direction, and the stiffness constants were numerically integrated and averaged along the length of the undulation. Third, the whole stiffness of filament winding composites was calculated through the transformed matrix between the principal coordinate axis and the direction of filament-winding. Some important changes exhibited by the stiffness matrices, especially the stiffness coupling effects due to the fiber undulation are obvious.
2010, 27(1): 185-189.
Abstract:
A methodology based on fabric microst ructure was built to calculate the micro geometric parameters and predict the fiber volume fraction. A mechanical model was also established to predict engineering elastic constants.The influence of various woven parameters on the elastic properties was examined and analysed. The edgewise tensile and flatwise compression experimental samples were fabricated and experiments were performed to validate the modeling method, good agreement between the theoretical predictions and the experimental results demonst rates that the proposed model is correct .
A methodology based on fabric microst ructure was built to calculate the micro geometric parameters and predict the fiber volume fraction. A mechanical model was also established to predict engineering elastic constants.The influence of various woven parameters on the elastic properties was examined and analysed. The edgewise tensile and flatwise compression experimental samples were fabricated and experiments were performed to validate the modeling method, good agreement between the theoretical predictions and the experimental results demonst rates that the proposed model is correct .
2010, 27(1): 190-195.
Abstract:
An interface element model based on the virtual crack closure technique (VCCT) was introduced to study the 2D delamination growth problem and predict the loading capacity of laminated composites. The interface elements were embedded along the potential crack path in advance to calculate the strain energy release rate and simulate the delamination growth of laminated composites in conjunction with the power law fracture criteria. The numerical errors induced by the different lengths of the element s at the crack tip had been corrected to minimize the negative effect of change in mesh density on numerical results. The double cantilever beam (DCB), end notch flexure (NEF) and mixed mode bending (MMB) models were taken to validate this approach. The results of the FE simulation agree well with the analytical solutions. It confirms that the approach is reliable and feasible for modeling the delamination growth in laminated composites. Three composite T-joints with different flaws were numerically simulated with the interface elements. Excellent agreement was found between the numerical results and the experimental data.
An interface element model based on the virtual crack closure technique (VCCT) was introduced to study the 2D delamination growth problem and predict the loading capacity of laminated composites. The interface elements were embedded along the potential crack path in advance to calculate the strain energy release rate and simulate the delamination growth of laminated composites in conjunction with the power law fracture criteria. The numerical errors induced by the different lengths of the element s at the crack tip had been corrected to minimize the negative effect of change in mesh density on numerical results. The double cantilever beam (DCB), end notch flexure (NEF) and mixed mode bending (MMB) models were taken to validate this approach. The results of the FE simulation agree well with the analytical solutions. It confirms that the approach is reliable and feasible for modeling the delamination growth in laminated composites. Three composite T-joints with different flaws were numerically simulated with the interface elements. Excellent agreement was found between the numerical results and the experimental data.
2010, 27(1): 196-201.
Abstract:
In order to analyze the sensitivity coefficient s of piezoelectric lamina in terms of Hamilton canonical equation, based on the H-R ( Hellinger-Reissner) variational principle of piezoelectric materials, the expression of operator was deduced for Hamilton canonical equation, and the governing equations of static response were established for piezoelectric plates simply supported on four sides as well. According to the definition of sensitivity analysis, the hybrid governing equation of static response and sensitivity coefficient s was obtained by uniting Hamilton canonical equation and the equation of sensitivity. The mechanic, electric parameters and the sensitivity coefficients of static response would be gained by this hybrid governing equations at the same time. This algorithm simplifies the process and improves the efficiency of calculation and stability. The result s of numerical examples, compared with those of the finite difference methods, show that the present solution is efficient.
In order to analyze the sensitivity coefficient s of piezoelectric lamina in terms of Hamilton canonical equation, based on the H-R ( Hellinger-Reissner) variational principle of piezoelectric materials, the expression of operator was deduced for Hamilton canonical equation, and the governing equations of static response were established for piezoelectric plates simply supported on four sides as well. According to the definition of sensitivity analysis, the hybrid governing equation of static response and sensitivity coefficient s was obtained by uniting Hamilton canonical equation and the equation of sensitivity. The mechanic, electric parameters and the sensitivity coefficients of static response would be gained by this hybrid governing equations at the same time. This algorithm simplifies the process and improves the efficiency of calculation and stability. The result s of numerical examples, compared with those of the finite difference methods, show that the present solution is efficient.
