2003 Vol. 20, No. 5
2003, 20(5): 1-7.
Abstract:
The microstructural evolution of SiCP/ZA27 composite modified by Zr during partial remelting was investigated using back-scattered electron imaging technique in scanning electron microscopy (SEM), and also compared with that of the not modified SiCP/ZA27 composite as well as that of the monolithic ZA27 alloy. The results indicated that the matrix microstructure of the composite modified by 0.2 wt% Zr experienced in succession the rapid merging of the secondary dendritic arms and the resulting growth of the primary dendrites, the melting of the interdendritic regions and resulting in the separation of the microstructure, and finally formed the slurry needed by thixoforming with the uniform, small and globular solid particles through the spheroidization during heating at 460℃ (0min~30min). No obvious coalescence of the solid particles was found during the subsequent isothermal holding (30 min~80 min). The primary dendrites of the not modified composite changed into interconnected and irregular grains during the heating stage and did not spheroidize completely even when holding for 80 min. The separation of the microstructure of the monolithic alloy was faster than that of the modified composite during the initial stage, but the particle coalescence was likely more obvious during the subsequent holding period. The rapid coalescence of the primary dendrites during the initial stage of the heating resulted from the diffusion of the interdendritic eutectics towards the dendrites. In addition, the microstructural evolution was also discussed through analyzing the phase transformations which occurred during this process.
The microstructural evolution of SiCP/ZA27 composite modified by Zr during partial remelting was investigated using back-scattered electron imaging technique in scanning electron microscopy (SEM), and also compared with that of the not modified SiCP/ZA27 composite as well as that of the monolithic ZA27 alloy. The results indicated that the matrix microstructure of the composite modified by 0.2 wt% Zr experienced in succession the rapid merging of the secondary dendritic arms and the resulting growth of the primary dendrites, the melting of the interdendritic regions and resulting in the separation of the microstructure, and finally formed the slurry needed by thixoforming with the uniform, small and globular solid particles through the spheroidization during heating at 460℃ (0min~30min). No obvious coalescence of the solid particles was found during the subsequent isothermal holding (30 min~80 min). The primary dendrites of the not modified composite changed into interconnected and irregular grains during the heating stage and did not spheroidize completely even when holding for 80 min. The separation of the microstructure of the monolithic alloy was faster than that of the modified composite during the initial stage, but the particle coalescence was likely more obvious during the subsequent holding period. The rapid coalescence of the primary dendrites during the initial stage of the heating resulted from the diffusion of the interdendritic eutectics towards the dendrites. In addition, the microstructural evolution was also discussed through analyzing the phase transformations which occurred during this process.
2003, 20(5): 8-15.
Abstract:
Explosive consolidation technology is employed to prepare MoSi2P/Nb high-temperature composites. The microstructure features and mechanical properties of MoSi2P/Nb composites were also studied. The results show that there are three kind of microstructure features in the composites and the compactness of the composites increase from outer layer to inner layer. Cores of the composites exhibit as cast feature because the energy massed to the central of the powders. With increasing λ values, the compactness of MoSi2P/Nb composites increases——the relative density can reach as high as 95.4%. As a result, the compressive strength of the composites increases as λ increases. Based on the analysis, it is pointed out that the explosive consolidation technology can be used in the preparation of MoSi2P/Nb high-temperature composites.
Explosive consolidation technology is employed to prepare MoSi2P/Nb high-temperature composites. The microstructure features and mechanical properties of MoSi2P/Nb composites were also studied. The results show that there are three kind of microstructure features in the composites and the compactness of the composites increase from outer layer to inner layer. Cores of the composites exhibit as cast feature because the energy massed to the central of the powders. With increasing λ values, the compactness of MoSi2P/Nb composites increases——the relative density can reach as high as 95.4%. As a result, the compressive strength of the composites increases as λ increases. Based on the analysis, it is pointed out that the explosive consolidation technology can be used in the preparation of MoSi2P/Nb high-temperature composites.
2003, 20(5): 16-21.
Abstract:
Four kinds of ceramic particles of WC,ZrO2,Cr2O3 and Al2O3 were used as an reinforced phase and the nickel alloy powder as a matrix, the erosive wear properties of four types of composite coatings fabricated with plasma spraying were experimentally studied with the wear test equipment. The erosion surface characteristics of composite coating were measured by means of the surface appearance measuring meter. The effects of the ceramic particle volume fraction, abrasive particle size, impinging angle and velocity on the erosion loss of ceramic particles/nickel alloy composite coatings were investigated with the orthogonal test method. The empirical equations of the erosion loss weight are obtained for the WC,ZrO2,Cr2O3 and Al2O3 particles/nickel alloy composite coatings with the multiple regression method.
Four kinds of ceramic particles of WC,ZrO2,Cr2O3 and Al2O3 were used as an reinforced phase and the nickel alloy powder as a matrix, the erosive wear properties of four types of composite coatings fabricated with plasma spraying were experimentally studied with the wear test equipment. The erosion surface characteristics of composite coating were measured by means of the surface appearance measuring meter. The effects of the ceramic particle volume fraction, abrasive particle size, impinging angle and velocity on the erosion loss of ceramic particles/nickel alloy composite coatings were investigated with the orthogonal test method. The empirical equations of the erosion loss weight are obtained for the WC,ZrO2,Cr2O3 and Al2O3 particles/nickel alloy composite coatings with the multiple regression method.
2003, 20(5): 22-27.
Abstract:
The liquid encapsulated approach was used in rare-earth modification on the surface of α-Al2O3 micro powder in this paper. Then the aluminum matrix composite reinforced by the α-Al2O3 particles that had been modified by Y2O3 was fabricated using the squeeze-casting technique. And the microstructure and tensile properties of the composites were analysed and studied. The result showed that α-Al2O3 micro powders modified by Y2O3 were distributed uniformly in the aluminum liquid. The interfacial wettability was improved. The microstructure of the composites was more even.The TEM observation showed that the α-Al2O3 powders were encapsulated homogeneously. EDAX analysis indicated that the powder surfaces included high content of Y and Al elements. And the diffraction peak of Y2O3 was also found in the X-ray diffraction spectrum graph. The tensile testing indicated that the strengthening effect of the modified-Al2O3 on Al alloy was improved obviously and the tensile strength of composites was improved 29.8 %,the yield strength was increased 38.4 % and the elongation was ncreased 10.3 %.The SEM analysis of the fracture indicated that the dimples of the modified-Al2O3P/6061Al composites were more even and the material embodied good plastics.
The liquid encapsulated approach was used in rare-earth modification on the surface of α-Al2O3 micro powder in this paper. Then the aluminum matrix composite reinforced by the α-Al2O3 particles that had been modified by Y2O3 was fabricated using the squeeze-casting technique. And the microstructure and tensile properties of the composites were analysed and studied. The result showed that α-Al2O3 micro powders modified by Y2O3 were distributed uniformly in the aluminum liquid. The interfacial wettability was improved. The microstructure of the composites was more even.The TEM observation showed that the α-Al2O3 powders were encapsulated homogeneously. EDAX analysis indicated that the powder surfaces included high content of Y and Al elements. And the diffraction peak of Y2O3 was also found in the X-ray diffraction spectrum graph. The tensile testing indicated that the strengthening effect of the modified-Al2O3 on Al alloy was improved obviously and the tensile strength of composites was improved 29.8 %,the yield strength was increased 38.4 % and the elongation was ncreased 10.3 %.The SEM analysis of the fracture indicated that the dimples of the modified-Al2O3P/6061Al composites were more even and the material embodied good plastics.
2003, 20(5): 28-32.
Abstract:
Utilizing self-made centrifugal high-speed electroplating equipment, the effects of technological parameters, such as temperature, pH value, current density, SiC content in electrolyte, and rotation speed of cathode, on SiC content in SiC/Ni composite coating are studied. The distribution of SiC particles in composite coating and the coating performance are also investigated. Experimental results show that temperature, current density, SiC content in electrolyte, and cathode rotation speed influence SiC codeposition volume obviously, while the pH value has little influence on SiC codeposition volume. SiC/Ni composite coating with well-distribution and high SiC codeposition volume can be prepared utilizing the centrifugal high-speed electeoplating equipment. The high codeposition amount of composite coating provides high hardness and wearability.
Utilizing self-made centrifugal high-speed electroplating equipment, the effects of technological parameters, such as temperature, pH value, current density, SiC content in electrolyte, and rotation speed of cathode, on SiC content in SiC/Ni composite coating are studied. The distribution of SiC particles in composite coating and the coating performance are also investigated. Experimental results show that temperature, current density, SiC content in electrolyte, and cathode rotation speed influence SiC codeposition volume obviously, while the pH value has little influence on SiC codeposition volume. SiC/Ni composite coating with well-distribution and high SiC codeposition volume can be prepared utilizing the centrifugal high-speed electeoplating equipment. The high codeposition amount of composite coating provides high hardness and wearability.
2003, 20(5): 33-38.
Abstract:
Combustion reaction welding technique was used for welding TiB2 and metal(Mo). The results showed that the main products of combustion reaction were TiB2 and MoB. When the content of Mo in intermediums was over 60 wt%, Mo would be surplus. Temperature strongly affected samples properties. When the sample was welded at 1500 ℃ with 80 wt% Mo in the intermedium, the value of bending strength was the largest. The largest value of shear strength among all the samples was the one welded at 1500 ℃ with 40 wt% Mo in the intermedium.
Combustion reaction welding technique was used for welding TiB2 and metal(Mo). The results showed that the main products of combustion reaction were TiB2 and MoB. When the content of Mo in intermediums was over 60 wt%, Mo would be surplus. Temperature strongly affected samples properties. When the sample was welded at 1500 ℃ with 80 wt% Mo in the intermedium, the value of bending strength was the largest. The largest value of shear strength among all the samples was the one welded at 1500 ℃ with 40 wt% Mo in the intermedium.
2003, 20(5): 39-43.
Abstract:
Vitrified bond cubic boron nitride (CBN) grinding tools are new ceramic/glass composites for grinding. This paper discussed the manufacturing principles of these materials in terms of composites theory and prepared such materials experimentally with success. The results showed that the suitable sintering temperature of vitrified bond CBN grinding tools should be lower than 800 ℃. The strength of vitrified bond CBN grinding tools was obviously affected by the difference of thermal expansion coefficient between vitrified bond and CBN abrasives. C1 bond was more suitable for the manufacturing of vitrified bond CBN grinding tools. Within the sintering temperature range, relatively higher sintering temperature was beneficial to the strength of the bond bridge and the holding strength between bond and CBN abrasive particles.
Vitrified bond cubic boron nitride (CBN) grinding tools are new ceramic/glass composites for grinding. This paper discussed the manufacturing principles of these materials in terms of composites theory and prepared such materials experimentally with success. The results showed that the suitable sintering temperature of vitrified bond CBN grinding tools should be lower than 800 ℃. The strength of vitrified bond CBN grinding tools was obviously affected by the difference of thermal expansion coefficient between vitrified bond and CBN abrasives. C1 bond was more suitable for the manufacturing of vitrified bond CBN grinding tools. Within the sintering temperature range, relatively higher sintering temperature was beneficial to the strength of the bond bridge and the holding strength between bond and CBN abrasive particles.
2003, 20(5): 44-48.
Abstract:
Three-dimensional braided carbon fiber reinforced silicon carbide(3D-B Cf/SiC) composites were fabricated via polycarbosilane (PCS) precursor infiltration and pyrolysis processing assisted by hot-pressing. The influences of hot-pressing processing on the densities and mechanical properties of 3D-B Cf/SiC composites were studied. The results showed that the densities and mechanical properties of the composites were enhanced greatly by using hot-pressing processing after the first precursor infiltration during the fabricating of Ceramic Matrix Composites. The density,flexural strength,fracture toughness and shear strength of the composites, which were hot-pressed at 1600℃ for 1hour with a pressure of 10MPa in the first pyrolysis cycle and treated subsequently with six times of PCS precursor infiltration and pyrolysis under atmospheric pressure, were 1.79 g/cm3,672MPa,18.9MPa·m1/2 and about 50MPa, respectively. The composites had good heat shock resistance and high temperature oxidation resistance.
Three-dimensional braided carbon fiber reinforced silicon carbide(3D-B Cf/SiC) composites were fabricated via polycarbosilane (PCS) precursor infiltration and pyrolysis processing assisted by hot-pressing. The influences of hot-pressing processing on the densities and mechanical properties of 3D-B Cf/SiC composites were studied. The results showed that the densities and mechanical properties of the composites were enhanced greatly by using hot-pressing processing after the first precursor infiltration during the fabricating of Ceramic Matrix Composites. The density,flexural strength,fracture toughness and shear strength of the composites, which were hot-pressed at 1600℃ for 1hour with a pressure of 10MPa in the first pyrolysis cycle and treated subsequently with six times of PCS precursor infiltration and pyrolysis under atmospheric pressure, were 1.79 g/cm3,672MPa,18.9MPa·m1/2 and about 50MPa, respectively. The composites had good heat shock resistance and high temperature oxidation resistance.
2003, 20(5): 49-52.
Abstract:
The weak impregnation will result in the formation of traps in the composites because the impregnation of the resin to fiber reinforcement is one of the major factors during the filling process of RTM. It will degrade interfacial performance of the composites. In this paper, cold plasma technology is used to treat the surface of carbon fibers braided by PET and the surface microstructure of the carbon fiber is analyzed by AFM. The result shows that cold plasma treatment improves the surface polarity of the carbon fiber, which enhances the impregnation of the carbon fiber braided by PET during the resin flowing process and improves the interfacial properties of RTM composites.
The weak impregnation will result in the formation of traps in the composites because the impregnation of the resin to fiber reinforcement is one of the major factors during the filling process of RTM. It will degrade interfacial performance of the composites. In this paper, cold plasma technology is used to treat the surface of carbon fibers braided by PET and the surface microstructure of the carbon fiber is analyzed by AFM. The result shows that cold plasma treatment improves the surface polarity of the carbon fiber, which enhances the impregnation of the carbon fiber braided by PET during the resin flowing process and improves the interfacial properties of RTM composites.
2003, 20(5): 53-56.
Abstract:
Phenyl vinyl compounds(styrene and divinyl styrene) modified bisphenol A dicyanate ester resin (BADCy) has been studied in this paper. The composition of the resin matrix has been selected according to a triangular optimization method as well as the experiment result. The phase separation of modified resin matrix at temperatures below 40℃ has been resolved by adding a little molecule substance containing oxygen atoms. At the same time, the storage stability has been prolongated efficiently. The modified resin system is suitable for RTM process at room temperature.
Phenyl vinyl compounds(styrene and divinyl styrene) modified bisphenol A dicyanate ester resin (BADCy) has been studied in this paper. The composition of the resin matrix has been selected according to a triangular optimization method as well as the experiment result. The phase separation of modified resin matrix at temperatures below 40℃ has been resolved by adding a little molecule substance containing oxygen atoms. At the same time, the storage stability has been prolongated efficiently. The modified resin system is suitable for RTM process at room temperature.
2003, 20(5): 57-62.
Abstract:
Nanocomposites based on rectorite(REC) and thermoplastic polyurethane rubber(TPUR) were prepared successfully by a melt-processed intercalation method aiming at improving the mechanical properties. The results have shown that organic treating agents such as dodecyl aryl ammonium salt (C12), hexadecyl ammonium salt (C16), benzidine(BZD), etc. play a critical role on REC and the resulting composites. Several kinds of organic REC (termed as C12-REC,C16-REC and BZD-REC,respectively) were prepared for comparison, and C12-REC has the best miscibility and dispersibility in TPUR. Tensile properties measurements of REC/TPUR indicate that the addition of about 2 wt% of C12-REC can increase tensile strength and tear strength up to 57.93 MPa and 123.37kN/m, which are about 49% and 33% higher than those of pure TPUR, respectively. Besides, the influences of REC's treating conditions on nanocomposites' mechanical properties are basically investigated, and it is found that the best treating time to prepare organic REC is 2 h.
Nanocomposites based on rectorite(REC) and thermoplastic polyurethane rubber(TPUR) were prepared successfully by a melt-processed intercalation method aiming at improving the mechanical properties. The results have shown that organic treating agents such as dodecyl aryl ammonium salt (C12), hexadecyl ammonium salt (C16), benzidine(BZD), etc. play a critical role on REC and the resulting composites. Several kinds of organic REC (termed as C12-REC,C16-REC and BZD-REC,respectively) were prepared for comparison, and C12-REC has the best miscibility and dispersibility in TPUR. Tensile properties measurements of REC/TPUR indicate that the addition of about 2 wt% of C12-REC can increase tensile strength and tear strength up to 57.93 MPa and 123.37kN/m, which are about 49% and 33% higher than those of pure TPUR, respectively. Besides, the influences of REC's treating conditions on nanocomposites' mechanical properties are basically investigated, and it is found that the best treating time to prepare organic REC is 2 h.
2003, 20(5): 63-67.
Abstract:
Microwave absorbing properties of carbon fiber felt and parallel-arranged carbon fiber composites were investigated respectively. The results show that the absorbing properties of parallel-arranged composites were affected greatly by the distance and content of carbon fibers. In this research, the composites obtained a reflection loss above 10 dB over 3 GHz bandwidth. The carbon fiber felt materials exhibited promising characteristics of absorption over the frequency range of 8 GHz~18 GHz with 0.27 wt% felt. The properties were affected mainly by the content of felt.
Microwave absorbing properties of carbon fiber felt and parallel-arranged carbon fiber composites were investigated respectively. The results show that the absorbing properties of parallel-arranged composites were affected greatly by the distance and content of carbon fibers. In this research, the composites obtained a reflection loss above 10 dB over 3 GHz bandwidth. The carbon fiber felt materials exhibited promising characteristics of absorption over the frequency range of 8 GHz~18 GHz with 0.27 wt% felt. The properties were affected mainly by the content of felt.
2003, 20(5): 68-72.
Abstract:
In this work, the composites consisting of continuous PAN-based carbon fibers and vinyl ester resins were fabricated by pultrusion processing, in which on-line surface treatment on the carbon fibers by thermal oxidization was carried out. The microstructures of the surfaces of both treated and untreated carbon fibers and the fracture morphologies of the composites were analyzed by using SEM. Also, the quasi-static mechanical properties and the thermodynamic mechanical properties of the composites were measured with Universal Materials Tester and Dynamic Mechanical Thermal Analyzer (DMTA), respectively. The results show that the surface roughness of the carbon fibers increases by the surface treatment, and thus the interfacial adhesion between the carbon fibers and the vinyl ester resins rises, and the mechanical properties, especially the Interlaminar Shear Strength (ILSS), of the composites are obviously improved. Moreover, according to the thermodynamic mechanical properties of the composites, it is found that the improvement of interface properties causes the loss modulus reduced, and can increase the fatigue resistance of the composites.
In this work, the composites consisting of continuous PAN-based carbon fibers and vinyl ester resins were fabricated by pultrusion processing, in which on-line surface treatment on the carbon fibers by thermal oxidization was carried out. The microstructures of the surfaces of both treated and untreated carbon fibers and the fracture morphologies of the composites were analyzed by using SEM. Also, the quasi-static mechanical properties and the thermodynamic mechanical properties of the composites were measured with Universal Materials Tester and Dynamic Mechanical Thermal Analyzer (DMTA), respectively. The results show that the surface roughness of the carbon fibers increases by the surface treatment, and thus the interfacial adhesion between the carbon fibers and the vinyl ester resins rises, and the mechanical properties, especially the Interlaminar Shear Strength (ILSS), of the composites are obviously improved. Moreover, according to the thermodynamic mechanical properties of the composites, it is found that the improvement of interface properties causes the loss modulus reduced, and can increase the fatigue resistance of the composites.
2003, 20(5): 73-76.
Abstract:
The relation between dynamic changes of curing degree and temperature is intensively coupled during the modeling process of polymer composite materials. On the basis of curing kinetics and thermal conduction theories, a mathematical model about temperature distribution and curing degree variation is established in this paper. Kinetics parameters based on the models are determined by using differential scanning calorimetry(DSC). A numerical model about temperature and curing degree was developed by combining the two-dimensional finite element with finite difference, and the coupled question is solved by using Euler step-by-step iterative method. The computer code is worked out according to the established model to simulate the distribution of temperature and curing degree closed to the test result, which provides the theoretical basis for optimizing practical process parameters.
The relation between dynamic changes of curing degree and temperature is intensively coupled during the modeling process of polymer composite materials. On the basis of curing kinetics and thermal conduction theories, a mathematical model about temperature distribution and curing degree variation is established in this paper. Kinetics parameters based on the models are determined by using differential scanning calorimetry(DSC). A numerical model about temperature and curing degree was developed by combining the two-dimensional finite element with finite difference, and the coupled question is solved by using Euler step-by-step iterative method. The computer code is worked out according to the established model to simulate the distribution of temperature and curing degree closed to the test result, which provides the theoretical basis for optimizing practical process parameters.
2003, 20(5): 77-81.
Abstract:
Poly (vinyl butyral)/ Silica nanocomposite materials in which the content of nanosized silica is varied from 2 wt% to 16 wt% were prepared by a co-mixing process. The microstructure, morphology and optical properties of the composites were studied by UV-VIS, FT-IR, SEM and XRD. The results showed that the silica forms nanometer microphase with the diameter from about 30 nm to 50 nm and disperses in the poly (vinyl butyral) matrix. It is found that ultraviolet rays from 290 nm to 400 nm can be effectively absorbed and shielded by the transparent resin membrane made from the PVB/SiO2 nanocomposites. The mechanical properties of the composites were also investigated, and the results were obtained in the elongation at break that is 18 % and 148 % for PVB materials and PVB/SiO2 nanocomposites, respectively. Meanwhile,the current technique is characterized by many advantages, such as simple, low cost, easy to be controlled and broader applicability.
Poly (vinyl butyral)/ Silica nanocomposite materials in which the content of nanosized silica is varied from 2 wt% to 16 wt% were prepared by a co-mixing process. The microstructure, morphology and optical properties of the composites were studied by UV-VIS, FT-IR, SEM and XRD. The results showed that the silica forms nanometer microphase with the diameter from about 30 nm to 50 nm and disperses in the poly (vinyl butyral) matrix. It is found that ultraviolet rays from 290 nm to 400 nm can be effectively absorbed and shielded by the transparent resin membrane made from the PVB/SiO2 nanocomposites. The mechanical properties of the composites were also investigated, and the results were obtained in the elongation at break that is 18 % and 148 % for PVB materials and PVB/SiO2 nanocomposites, respectively. Meanwhile,the current technique is characterized by many advantages, such as simple, low cost, easy to be controlled and broader applicability.
2003, 20(5): 82-87.
Abstract:
Layered Double Hydroxide (LDH) was synthesized and modified with different coupling agents, then modified LDH as heat stabilizer was filled into polyvinyl chloride (PVC) to form composite materials. Samples were characterized by XRD, IR, TEM and Particle Size Analysis. The results showed that dispersion properties of LDH in PVC were improved, and mechanical properties and heat stability of LDH/PVC composite materials were prompted.
Layered Double Hydroxide (LDH) was synthesized and modified with different coupling agents, then modified LDH as heat stabilizer was filled into polyvinyl chloride (PVC) to form composite materials. Samples were characterized by XRD, IR, TEM and Particle Size Analysis. The results showed that dispersion properties of LDH in PVC were improved, and mechanical properties and heat stability of LDH/PVC composite materials were prompted.
2003, 20(5): 88-94.
Abstract:
Based on a novel nano-TiO2 powder, Polypropylene/TiO2 composites was made by direct melt blending. The morphology, crystallization, mechanical properties, antimicrobial properties, rheological properties of the new composites were investigated. The results showed that the novel TiO2 nano-powder dispersed well in PP matrix; the sizes of most agglomerates nearly reached 100 nm; TiO2 nano-powder could induce crystallization of PP, however, the crystallinity of PP decreased some; tensile strength and elongation of composites declined while modulus and impact strength of composites rose with the loading of nano-powder; nano-TiO2/PP composites with 2% loading of powder demonstrated an overall excellent mechanical properties. The novel composites have high antimicrobial properties, better flow ability than PP due to degradation of PP caused by the oxidation effect of nano-TiO2.
Based on a novel nano-TiO2 powder, Polypropylene/TiO2 composites was made by direct melt blending. The morphology, crystallization, mechanical properties, antimicrobial properties, rheological properties of the new composites were investigated. The results showed that the novel TiO2 nano-powder dispersed well in PP matrix; the sizes of most agglomerates nearly reached 100 nm; TiO2 nano-powder could induce crystallization of PP, however, the crystallinity of PP decreased some; tensile strength and elongation of composites declined while modulus and impact strength of composites rose with the loading of nano-powder; nano-TiO2/PP composites with 2% loading of powder demonstrated an overall excellent mechanical properties. The novel composites have high antimicrobial properties, better flow ability than PP due to degradation of PP caused by the oxidation effect of nano-TiO2.
2003, 20(5): 95-99.
Abstract:
Multi-ring pressfit is one effective way of solving the problem that the radial strength of composite flywheel is too low. A simplified model about the plane stress is adopted in this paper. Considering the increase of actual misfit in the pressfit, a method of calculating the stress of the multi-ring flywheel subjected to misfit is proposed. Based on the theory of stack, an approach of calculating the stress of the multi-ring flywheel subjected to centrifugal load is advanced. To ensure the flywheel against from separation, the concept and calculation of an interrelated critical rotating speed are introduced. The results showed that the effect of deformation in the pressfit on the stress of a flywheel subjected to misfit could not be neglected, the misfit and ring number having close relation with the stress and interrelated critical rotating speed of the flywheel.
Multi-ring pressfit is one effective way of solving the problem that the radial strength of composite flywheel is too low. A simplified model about the plane stress is adopted in this paper. Considering the increase of actual misfit in the pressfit, a method of calculating the stress of the multi-ring flywheel subjected to misfit is proposed. Based on the theory of stack, an approach of calculating the stress of the multi-ring flywheel subjected to centrifugal load is advanced. To ensure the flywheel against from separation, the concept and calculation of an interrelated critical rotating speed are introduced. The results showed that the effect of deformation in the pressfit on the stress of a flywheel subjected to misfit could not be neglected, the misfit and ring number having close relation with the stress and interrelated critical rotating speed of the flywheel.
2003, 20(5): 100-107.
Abstract:
A new type of actuator using functionally graded piezoelectric ceramics can produce large out of plane displacements, reduce mid-plane stresses and avoid failure from internal debonding or from stress peaks. A functionally graded piezoelectric ultrasound transducer has a broadband frequency characteristic. This study presents a simple and accurate high order theory to examine the electromechanical behaviour of piezoelectric generic shells with thickness-graded material properties. The displacement components are assumed to be a linear function of the shell thickness, while the electric potential is taken as a quadratic distribution through the thickness coordinate. Both equations of motion and boundary conditions of the shells are simultaneously obtained using the variational principle. Different types of charge equilibrium equations are considered, which correspond to the respective driving power when it is acted as actuators. The Fourier series method is then applied to obtain the analytical solution of mechanical and electric fields of functionally graded piezoelectric shells. These newly derived equations can be reduced to many typical structures as beam, plate and circular cylindrical shell. In terms of analyzing a simply-supported inhomogeneous and laminated piezoelectric plate, numerical results of the proposed formulation coincide well with exact solutions in previous literature. Finally, numerical studies are performed to examine the electromechanical responses of functionally graded piezoelectric circular cylindrical shells. The effects of graded material properties on the displacement, stresses and electric potential are clearly exhibited. This piece of work was motivated by the increased general use of functionally graded materials and piezoelectric materials and also a need to understand the electromechanical behaviour of functionally graded piezoelectric materials.
A new type of actuator using functionally graded piezoelectric ceramics can produce large out of plane displacements, reduce mid-plane stresses and avoid failure from internal debonding or from stress peaks. A functionally graded piezoelectric ultrasound transducer has a broadband frequency characteristic. This study presents a simple and accurate high order theory to examine the electromechanical behaviour of piezoelectric generic shells with thickness-graded material properties. The displacement components are assumed to be a linear function of the shell thickness, while the electric potential is taken as a quadratic distribution through the thickness coordinate. Both equations of motion and boundary conditions of the shells are simultaneously obtained using the variational principle. Different types of charge equilibrium equations are considered, which correspond to the respective driving power when it is acted as actuators. The Fourier series method is then applied to obtain the analytical solution of mechanical and electric fields of functionally graded piezoelectric shells. These newly derived equations can be reduced to many typical structures as beam, plate and circular cylindrical shell. In terms of analyzing a simply-supported inhomogeneous and laminated piezoelectric plate, numerical results of the proposed formulation coincide well with exact solutions in previous literature. Finally, numerical studies are performed to examine the electromechanical responses of functionally graded piezoelectric circular cylindrical shells. The effects of graded material properties on the displacement, stresses and electric potential are clearly exhibited. This piece of work was motivated by the increased general use of functionally graded materials and piezoelectric materials and also a need to understand the electromechanical behaviour of functionally graded piezoelectric materials.
2003, 20(5): 108-113.
Abstract:
Following the geometric pattern of the constituent yarn systems in 3D woven structures, a general purpose geometric cell model is developed. The length and orientation angle of the constituent yarns in each yarn system within a unit cell are calculated, and then the fiber volume fraction of 3D woven composites can be obtained. To verify the geometric model, samples of 3D woven composites with 11 various binding patterns are selected and the fiber volume fraction is measured. Experiment results are in good agreement with the outcomes of the model. Further, the geometrical model is used to discuss the effects of the binding pattern on the fiber volume fraction and yarn's orientation angle. It shows that a layer-to-layer binding can offer a higher degree of fiber volume fraction than a through-thickness binding, and that binders of an orthogonal interlock binding have a greater orientation angle than that of an angle interlock, indicating a more efficient reinforcement in the thickness direction of 3D woven composites.
Following the geometric pattern of the constituent yarn systems in 3D woven structures, a general purpose geometric cell model is developed. The length and orientation angle of the constituent yarns in each yarn system within a unit cell are calculated, and then the fiber volume fraction of 3D woven composites can be obtained. To verify the geometric model, samples of 3D woven composites with 11 various binding patterns are selected and the fiber volume fraction is measured. Experiment results are in good agreement with the outcomes of the model. Further, the geometrical model is used to discuss the effects of the binding pattern on the fiber volume fraction and yarn's orientation angle. It shows that a layer-to-layer binding can offer a higher degree of fiber volume fraction than a through-thickness binding, and that binders of an orthogonal interlock binding have a greater orientation angle than that of an angle interlock, indicating a more efficient reinforcement in the thickness direction of 3D woven composites.
2003, 20(5): 114-122.
Abstract:
A multiphase model has been developed and applied to two dimension solidification processing of Al-7 wet pct Si/SiC particles Fgm on different cooling conditions. Solidification processings of no particle, small particle and large particle by cooling on the top, the bottom, side face and four sides are researched. It is approved that there is negative macrosegregation on the field solidified first and positive macrosegregation on the field solidified later. There is macrosegregation of pattern A by cooling on the top and bottom and macrosegregation of pattern V by cooling on the side face and four sides. Scheil equation is approved. The creation of eutectic is affected by species macrosegregation, and the accumulation of large particles restrains the creation of eutectic.
A multiphase model has been developed and applied to two dimension solidification processing of Al-7 wet pct Si/SiC particles Fgm on different cooling conditions. Solidification processings of no particle, small particle and large particle by cooling on the top, the bottom, side face and four sides are researched. It is approved that there is negative macrosegregation on the field solidified first and positive macrosegregation on the field solidified later. There is macrosegregation of pattern A by cooling on the top and bottom and macrosegregation of pattern V by cooling on the side face and four sides. Scheil equation is approved. The creation of eutectic is affected by species macrosegregation, and the accumulation of large particles restrains the creation of eutectic.
2003, 20(5): 123-129.
Abstract:
A new bending model for angle-ply laminated plates is developed. Two series of in-plane displacement distributions in the thickness direction are derived by use of the sectional warping corrective theory, and hierarchical displacement functions are adopted in the length direction. Finally, based on the principle of minimum potential theory, special finite element models for cylindrical bending are obtained. Accuracy and convergence of the solution are studied, and the present results are compared with those of the existing first-order theory and higher-order theory. It is shown that the present stresses result is in good agreement with the exact solution, and the effectiveness of the present model for analyzing cylindrical bending is ascertained. The present model is simple while the freedoms are lower than those of other numerical methods.
A new bending model for angle-ply laminated plates is developed. Two series of in-plane displacement distributions in the thickness direction are derived by use of the sectional warping corrective theory, and hierarchical displacement functions are adopted in the length direction. Finally, based on the principle of minimum potential theory, special finite element models for cylindrical bending are obtained. Accuracy and convergence of the solution are studied, and the present results are compared with those of the existing first-order theory and higher-order theory. It is shown that the present stresses result is in good agreement with the exact solution, and the effectiveness of the present model for analyzing cylindrical bending is ascertained. The present model is simple while the freedoms are lower than those of other numerical methods.
2003, 20(5): 130-134.
Abstract:
For 3D braided CMC owing to interfacial fracture, it is remarkable that interfacial fracture mode mixing Ψ works on the material fracture toughness. Although the interfacial fracture mode mixing can hardly be determined because its expression involves an uncertain parameter-fracture length eigenvalue, the fracture mode mixing at the tip of crack Ψtip, which correlates with Ψ, can be decided uniquely. So the fracture toughness of 3D braided CMC material can be researched on interfacial cracks with Ψtip. By numerical simulation, this paper analyses the relation of the mixing Ψtip with the declining angle and interfacial thickness, further researches the influence of the 3D braided CMC's cracks path on the mixing Ψtip, and finds a way of fracture design of 3D braided CMC.
For 3D braided CMC owing to interfacial fracture, it is remarkable that interfacial fracture mode mixing Ψ works on the material fracture toughness. Although the interfacial fracture mode mixing can hardly be determined because its expression involves an uncertain parameter-fracture length eigenvalue, the fracture mode mixing at the tip of crack Ψtip, which correlates with Ψ, can be decided uniquely. So the fracture toughness of 3D braided CMC material can be researched on interfacial cracks with Ψtip. By numerical simulation, this paper analyses the relation of the mixing Ψtip with the declining angle and interfacial thickness, further researches the influence of the 3D braided CMC's cracks path on the mixing Ψtip, and finds a way of fracture design of 3D braided CMC.
2003, 20(5): 135-141.
Abstract:
Dynamic performance of a novel vibration isolator made of reinforced foam plastics is investigated in this paper. Experimental results show that, under steady periodic excitation, the isolator has strong nonlinear hysteretic characteristics, the restoring force of the isolator is influenced by the exciting frequency and vibration amplitude and is relative with the deformation history, and the shape of hysteretic loops of the restoring force is related to the stiffness and damping characteristics in the isolator. In view of the characteristics, a new smart idea of modeling is presented. According to the energy analysis, the restoring force can be decomposed into conservative force and non-conservative force, viz. elastic restoring force and damping force. The study has proved the idea of modeling is an ingenious one, which provides a useful means for modeling and parameters identification of the isolator. It lays a good foundation for dynamic design and dynamic optimization of the vibration isolator. The presented method can also be used for reference for other nonlinear hysteretic system analyses.
Dynamic performance of a novel vibration isolator made of reinforced foam plastics is investigated in this paper. Experimental results show that, under steady periodic excitation, the isolator has strong nonlinear hysteretic characteristics, the restoring force of the isolator is influenced by the exciting frequency and vibration amplitude and is relative with the deformation history, and the shape of hysteretic loops of the restoring force is related to the stiffness and damping characteristics in the isolator. In view of the characteristics, a new smart idea of modeling is presented. According to the energy analysis, the restoring force can be decomposed into conservative force and non-conservative force, viz. elastic restoring force and damping force. The study has proved the idea of modeling is an ingenious one, which provides a useful means for modeling and parameters identification of the isolator. It lays a good foundation for dynamic design and dynamic optimization of the vibration isolator. The presented method can also be used for reference for other nonlinear hysteretic system analyses.
2003, 20(5): 142-146.
Abstract:
Using the principle of superposition, the transverse loading state of a laminated curved beam with delaminations is divided into in mid-surface and out-off mid-surface loading states. Furthermore, the out-off mid-surface loading state is subdivided into the transverse loading state acting on a curved beam without delamination and the additional shear loading state which is applied along the delamination surfaces of the laminated beam. Therefore, the problem of delamination can be changed to the analysis about the additional displacements and stresses, which are caused by the additional shear loading. Then, a simple mechanics model about delamination is established. Finally, the analytical solutions of additional displacements and stresses are determined by the theory of engineering beam, and the stress intensity factor is obtained by the energy release rate method.
Using the principle of superposition, the transverse loading state of a laminated curved beam with delaminations is divided into in mid-surface and out-off mid-surface loading states. Furthermore, the out-off mid-surface loading state is subdivided into the transverse loading state acting on a curved beam without delamination and the additional shear loading state which is applied along the delamination surfaces of the laminated beam. Therefore, the problem of delamination can be changed to the analysis about the additional displacements and stresses, which are caused by the additional shear loading. Then, a simple mechanics model about delamination is established. Finally, the analytical solutions of additional displacements and stresses are determined by the theory of engineering beam, and the stress intensity factor is obtained by the energy release rate method.
2003, 20(5): 147-153.
Abstract:
Using the principle of superposition, the transverse loading state of a cylindrical shell with rectangular delaminations is decomposed, and the problem of delamination can be reduced to the analysis of an additional stress state of the original laminate subjected to additional shear load along the delamination surfaces. The laminate sections parallel to the boundary of the delamination area can be regarded as laminated beams with delaminations, the displacements in which can be expressed by the analytical solutions of additional displacements in the above beams. By this way, the additional displacement fields satisfying the displacement boundary conditions of the delamination area can be established. Finally, a closed form solution of additional displacements is obtained by the principle of minimum potential energy.
Using the principle of superposition, the transverse loading state of a cylindrical shell with rectangular delaminations is decomposed, and the problem of delamination can be reduced to the analysis of an additional stress state of the original laminate subjected to additional shear load along the delamination surfaces. The laminate sections parallel to the boundary of the delamination area can be regarded as laminated beams with delaminations, the displacements in which can be expressed by the analytical solutions of additional displacements in the above beams. By this way, the additional displacement fields satisfying the displacement boundary conditions of the delamination area can be established. Finally, a closed form solution of additional displacements is obtained by the principle of minimum potential energy.
