2002 Vol. 19, No. 3
2002, 19(3): 1-5.
Abstract:
Dynamic thermogravimetric analysis (TGA) of two kinds of cyanate/epoxy blends was performed. The effects of molar ratios of cyanate and epoxy on thermal stability were disclosed. Coats-Redfern Equation was used to compute the weight loss data and calculate the activation energies of decomposition. It is found that the cyanate-rich blends containing bisphenol A diglycidyl ether have a two step decomposition process and epoxy-rich blends have a single mechanism. The activation energy of thermal decomposition of the blends containing novolac epoxy, which is greater than that of the blends containing bisphenol A diglycidyl ether, is independent of the temperature and concentration of the epoxy, indicating much better thermal stability than that of the blends containing bisphenol A diglycidyl ether.
Dynamic thermogravimetric analysis (TGA) of two kinds of cyanate/epoxy blends was performed. The effects of molar ratios of cyanate and epoxy on thermal stability were disclosed. Coats-Redfern Equation was used to compute the weight loss data and calculate the activation energies of decomposition. It is found that the cyanate-rich blends containing bisphenol A diglycidyl ether have a two step decomposition process and epoxy-rich blends have a single mechanism. The activation energy of thermal decomposition of the blends containing novolac epoxy, which is greater than that of the blends containing bisphenol A diglycidyl ether, is independent of the temperature and concentration of the epoxy, indicating much better thermal stability than that of the blends containing bisphenol A diglycidyl ether.
2002, 19(3): 6-9.
Abstract:
Uncatalyzed blends of bisphenol A dicyanate ester/epoxy novolac with different molar ratios were prepared. Hydrothermal ageing for times up to one month was performed and water take-up profiles of those blends were determined by a gravimetric method. It was found that the blends absorbed much less water than homopolycyanate when the molar fractions of the cyanate group in the blends were greater than 0.5. Dynamic mechanical analysis and FTIR determination were performed on virgin and aged samples. The results demonstrate that the hydrothermal ageing resistance of the blends is superior to that of homopolycyanate.
Uncatalyzed blends of bisphenol A dicyanate ester/epoxy novolac with different molar ratios were prepared. Hydrothermal ageing for times up to one month was performed and water take-up profiles of those blends were determined by a gravimetric method. It was found that the blends absorbed much less water than homopolycyanate when the molar fractions of the cyanate group in the blends were greater than 0.5. Dynamic mechanical analysis and FTIR determination were performed on virgin and aged samples. The results demonstrate that the hydrothermal ageing resistance of the blends is superior to that of homopolycyanate.
2002, 19(3): 10-15.
Abstract:
Dynamic mechanical analyses of EB-cured epoxy resin are made. Through the research on variation regularity of the gel fraction, damping factor and dynamic modulus for different samples, the influences of EB radiation dosage, initiator dosage and heating treatment on radiation curing reaction of epoxy resin were obtained. The gel fraction, glass transition temperature and high temperature modulus of the cured epoxy resin increase with the rising of radiation dosage and the increased extents are decrescent at high radiation dosage. The inhomogeneity degree of cross-linked structure is enhanced with the increasing radiation dosage. In low radiation dosage, the glass transition temperature and high temperature modulus of the cured epoxy resin increase with the enhanced initiator dosage. But when high dosage radiation is used, the optimal dosage of the initiator appears. When the EB-cured epoxy resin is heated, the cross-linking extent is enhanced. But when the temperature of heating treatment exceeds the thermal decomposition temperature of the initiator, the local cross-linking network formed from thermal curing reaction can exist in the resin system.
Dynamic mechanical analyses of EB-cured epoxy resin are made. Through the research on variation regularity of the gel fraction, damping factor and dynamic modulus for different samples, the influences of EB radiation dosage, initiator dosage and heating treatment on radiation curing reaction of epoxy resin were obtained. The gel fraction, glass transition temperature and high temperature modulus of the cured epoxy resin increase with the rising of radiation dosage and the increased extents are decrescent at high radiation dosage. The inhomogeneity degree of cross-linked structure is enhanced with the increasing radiation dosage. In low radiation dosage, the glass transition temperature and high temperature modulus of the cured epoxy resin increase with the enhanced initiator dosage. But when high dosage radiation is used, the optimal dosage of the initiator appears. When the EB-cured epoxy resin is heated, the cross-linking extent is enhanced. But when the temperature of heating treatment exceeds the thermal decomposition temperature of the initiator, the local cross-linking network formed from thermal curing reaction can exist in the resin system.
2002, 19(3): 16-20.
Abstract:
In order to improve the interfacial properties of EB cured composites, the carbon fibers were anodized and coated with an epoxy-based coupling agent. The influence of different electrolytes used in anodic oxidation on the carbon fiber properties was studied. The untreated and treated carbon fibers were investigated by SEM and XPS, and the contact angles were analyzed to better understand the surface properties of carbon fibers. The adhesion between carbon fibers and epoxy matrix was evaluated using interlaminar shear strength (ILSS) testing of the EB processed composite samples and compared with adhesion data for the same fiber in a thermally processed epoxy matrix. It is shown that the carbon fibers treated with acidic electrolyte improve ILSS of EB cured composites; on the other hand, the carbon fibers treated with basic electrolyte decrease ILSS of EB crued composites. The interfacial properties of EB cured carbon fiber reinforced epoxy matrix composites are improved after the carbon fibers have been double-treated.
In order to improve the interfacial properties of EB cured composites, the carbon fibers were anodized and coated with an epoxy-based coupling agent. The influence of different electrolytes used in anodic oxidation on the carbon fiber properties was studied. The untreated and treated carbon fibers were investigated by SEM and XPS, and the contact angles were analyzed to better understand the surface properties of carbon fibers. The adhesion between carbon fibers and epoxy matrix was evaluated using interlaminar shear strength (ILSS) testing of the EB processed composite samples and compared with adhesion data for the same fiber in a thermally processed epoxy matrix. It is shown that the carbon fibers treated with acidic electrolyte improve ILSS of EB cured composites; on the other hand, the carbon fibers treated with basic electrolyte decrease ILSS of EB crued composites. The interfacial properties of EB cured carbon fiber reinforced epoxy matrix composites are improved after the carbon fibers have been double-treated.
2002, 19(3): 21-28.
Abstract:
It is difficult to insure the quality of composites for the reason that there are complicated processes during curing process of composites. There is a We need to develop an advanced on-line monitoring system for the curing process of composites. It is feasible to develop fiber optic sensors to monitor the molding process of composite materials. As the development of fiber optic technologies, the physical parameters, chemical parameters and the mechanical parameters of composites during the molding process are mightily monitored. In this paper, the principle of sensing the molding process of composites by fiber optic is introduced. The feasibility of establishing the smart fiber optic-composites system is set forth. A sort of fiber optic sensor based on strength modulation is researched to monitor the process of composite during the curing process. The experiments were carried out in the laboratory and production field. It can monitor the curing process, including the lowest point of the resin matrix, the end point of curing process of composite material sensitively and precisely. The research results show that the technology can be applied to intelligently monitoring and controlling the molding process of composite materials. The successful application of the optic fiber monitoring system in the real production field shows that this technology has reached practicality ability.
It is difficult to insure the quality of composites for the reason that there are complicated processes during curing process of composites. There is a We need to develop an advanced on-line monitoring system for the curing process of composites. It is feasible to develop fiber optic sensors to monitor the molding process of composite materials. As the development of fiber optic technologies, the physical parameters, chemical parameters and the mechanical parameters of composites during the molding process are mightily monitored. In this paper, the principle of sensing the molding process of composites by fiber optic is introduced. The feasibility of establishing the smart fiber optic-composites system is set forth. A sort of fiber optic sensor based on strength modulation is researched to monitor the process of composite during the curing process. The experiments were carried out in the laboratory and production field. It can monitor the curing process, including the lowest point of the resin matrix, the end point of curing process of composite material sensitively and precisely. The research results show that the technology can be applied to intelligently monitoring and controlling the molding process of composite materials. The successful application of the optic fiber monitoring system in the real production field shows that this technology has reached practicality ability.
2002, 19(3): 29-32.
Abstract:
Gate/vent locations are one of the most important variables in RTM mold design. This paper proposed an approach to arrange the gates and vents based on the distance of the mesh. With the assumption that the resin first fills the nodes near the gates, the vent locations required to avoid trapping air bubbles were determined. The results show that the proposed approach is efficient and effective.
Gate/vent locations are one of the most important variables in RTM mold design. This paper proposed an approach to arrange the gates and vents based on the distance of the mesh. With the assumption that the resin first fills the nodes near the gates, the vent locations required to avoid trapping air bubbles were determined. The results show that the proposed approach is efficient and effective.
2002, 19(3): 33-36.
Abstract:
The application of Polypropylene (PP) is limited by its poor impact strength at low temperatures, which is frequently improved by the introduction of elastomers. However, a simultaneous decrease of stiffness of the overall blend is inevitable. In this research, PP/mPE blend was reinforced with short glass fiber (SGF). The dynamic properties of PP/mPE/SGF composites were examined by means of hysteresis measurement method with the Stepwise Load Increase Procedure and Single Load Level Procedure. The results show that PP/mPE/SGF composites have a very high dynamic modulus and dynamic load limit.
The application of Polypropylene (PP) is limited by its poor impact strength at low temperatures, which is frequently improved by the introduction of elastomers. However, a simultaneous decrease of stiffness of the overall blend is inevitable. In this research, PP/mPE blend was reinforced with short glass fiber (SGF). The dynamic properties of PP/mPE/SGF composites were examined by means of hysteresis measurement method with the Stepwise Load Increase Procedure and Single Load Level Procedure. The results show that PP/mPE/SGF composites have a very high dynamic modulus and dynamic load limit.
2002, 19(3): 37-41.
Abstract:
The recycle treatment of carbon fiber/phenolic composites is investigated. Using the supercritical water as the action agent,when the temperature was 400 ℃, the concentration of NaOH was 1 mol/L, the reaction time was 30 min, and the filling rate was 0.62, the rate of decomposition reached 75 %.The gas chromatography and mass spectrometry analysis of the decomposition product indicate that they are the substance containing the benzene structure where the content of phenol and methyl phenol is 33 %. The rate of decomposition increases with the increase of action temperature and time. The SEM analysis of the decomposed sample shows that the surface of fiber is smooth, which indicates the considerable decomposition effect.
The recycle treatment of carbon fiber/phenolic composites is investigated. Using the supercritical water as the action agent,when the temperature was 400 ℃, the concentration of NaOH was 1 mol/L, the reaction time was 30 min, and the filling rate was 0.62, the rate of decomposition reached 75 %.The gas chromatography and mass spectrometry analysis of the decomposition product indicate that they are the substance containing the benzene structure where the content of phenol and methyl phenol is 33 %. The rate of decomposition increases with the increase of action temperature and time. The SEM analysis of the decomposed sample shows that the surface of fiber is smooth, which indicates the considerable decomposition effect.
2002, 19(3): 42-45.
Abstract:
Montmorillonite/Polyimide (MMT/PI) nanocomposite film was prepared with pyromellitic dianhydride (PMDA) and dimethylacetamide (DAPE) as monomers, and organic montmorillonite (MMT) treated by 16-decyltrimethyl ammonium chloride as inorganic reinforcement. The microphase of the PI/MMT film was characterized with TEM, XRD, TGA, DSC, etc. The results show that the proper content of 16-MMT in the matrix can lead to a nanophase reinforcement (1~2 nm in thickness) dispersion system. It is interesting thatthere was some orientation behavior in the matrix after 16-MMT was delaminated into sheets.
Montmorillonite/Polyimide (MMT/PI) nanocomposite film was prepared with pyromellitic dianhydride (PMDA) and dimethylacetamide (DAPE) as monomers, and organic montmorillonite (MMT) treated by 16-decyltrimethyl ammonium chloride as inorganic reinforcement. The microphase of the PI/MMT film was characterized with TEM, XRD, TGA, DSC, etc. The results show that the proper content of 16-MMT in the matrix can lead to a nanophase reinforcement (1~2 nm in thickness) dispersion system. It is interesting thatthere was some orientation behavior in the matrix after 16-MMT was delaminated into sheets.
2002, 19(3): 46-50.
Abstract:
The reinforced mechanism of the polymer latex added in the steel fiber reinforced concrete was researched, based on mechanical experiments and photograph analysis of the Electron Spectroscopy of Chemical Analysis (ESCA) with Oxford Link300 and the Scanning Electron Microscopy with HITACHI S3500N. The results show that there is an optimum of the polymer added in the steel fiber reinforced concrete. And when it is added to the optimum, the polymer acts as a "bridge"; the "bridge" strengthens the physical absorption each other originally and makes them change into chemical absorption, thus improving the material properties of the whole system.
The reinforced mechanism of the polymer latex added in the steel fiber reinforced concrete was researched, based on mechanical experiments and photograph analysis of the Electron Spectroscopy of Chemical Analysis (ESCA) with Oxford Link300 and the Scanning Electron Microscopy with HITACHI S3500N. The results show that there is an optimum of the polymer added in the steel fiber reinforced concrete. And when it is added to the optimum, the polymer acts as a "bridge"; the "bridge" strengthens the physical absorption each other originally and makes them change into chemical absorption, thus improving the material properties of the whole system.
2002, 19(3): 51-55.
Abstract:
To investigate the composite repair effect for damaged aluminum alloy plates, the influences of different composite patches, bonding adhesives, surface treatment methods and repair bonding length on the repaired tensile strength of the holed aluminum plate are studied. The tensile strength of the repaired damaged or corroded aluminum alloy plate used on the planes was tested and the possibility to meet applicable requirements with composite patches was investigated. The results show that the repair methods adopted in the present study are effective.
To investigate the composite repair effect for damaged aluminum alloy plates, the influences of different composite patches, bonding adhesives, surface treatment methods and repair bonding length on the repaired tensile strength of the holed aluminum plate are studied. The tensile strength of the repaired damaged or corroded aluminum alloy plate used on the planes was tested and the possibility to meet applicable requirements with composite patches was investigated. The results show that the repair methods adopted in the present study are effective.
2002, 19(3): 56-60.
Abstract:
The dry sliding tribological characteristics were investigated with self-made block-disk tester of SiC particle-reinforced aluminum composites and gray cast iron (HT250) against semi-metallic frictional materials. The experimental results indicate that the wear rates of SiC particle reinforced composites are much less (the wear rate of Al-10%Si/30%SiC(14μm) is about one third of that of gray cast iron) than that of gray cast iron which are commonly used to make brake disks, while the frictional coefficient is about the same. Based on the experimental results, the authors suggest that SiC particle-reinforced aluminum-matrix composite be one of the suitable materials for making vehicle-braking components.
The dry sliding tribological characteristics were investigated with self-made block-disk tester of SiC particle-reinforced aluminum composites and gray cast iron (HT250) against semi-metallic frictional materials. The experimental results indicate that the wear rates of SiC particle reinforced composites are much less (the wear rate of Al-10%Si/30%SiC(14μm) is about one third of that of gray cast iron) than that of gray cast iron which are commonly used to make brake disks, while the frictional coefficient is about the same. Based on the experimental results, the authors suggest that SiC particle-reinforced aluminum-matrix composite be one of the suitable materials for making vehicle-braking components.
2002, 19(3): 61-65.
Abstract:
The aeural-fuzzy system has been applied to acquire the constitutive relationships of endogenetic particle distribution in FGM creating centrifugal casting at different mould temperatures, pouring temperatures and rotating speeds. During building up the neural-fuzzy model of the constitutive relationship for the alloy, mould temperature, pouring temperature and rotating speed were taken as the inputs while the relative thickness of the endogenetic particle distribution in FGM was taken as the output. Comparison of the predicted and experimental results shows that the neural-fuzzy system model used to predict the constitutive relationship of the endogenetic particle distribution in FGM creating centrifugal casting has good learning precision and good generalization. It is viable to forecast the endogenetic particle distribution in FGM creating centrifugal casting based on the neural-fuzzy system.
The aeural-fuzzy system has been applied to acquire the constitutive relationships of endogenetic particle distribution in FGM creating centrifugal casting at different mould temperatures, pouring temperatures and rotating speeds. During building up the neural-fuzzy model of the constitutive relationship for the alloy, mould temperature, pouring temperature and rotating speed were taken as the inputs while the relative thickness of the endogenetic particle distribution in FGM was taken as the output. Comparison of the predicted and experimental results shows that the neural-fuzzy system model used to predict the constitutive relationship of the endogenetic particle distribution in FGM creating centrifugal casting has good learning precision and good generalization. It is viable to forecast the endogenetic particle distribution in FGM creating centrifugal casting based on the neural-fuzzy system.
2002, 19(3): 66-69.
Abstract:
The martensitic transformation behaviors of TiNi shape memory alloy-cement composite are explored. The DSC results indicate that the reverse transformation temperature of the remained martensite increases due to the constraint of the cement matrix. In the beginning of the reverse martensitic transformation, the average reverse transformation ratio is larger. Above the finish temperature of the endothermic peak in the DSC heating curve of the cement composite sample, the reverse transformation of the remained martensite is still undergoing slowly.
The martensitic transformation behaviors of TiNi shape memory alloy-cement composite are explored. The DSC results indicate that the reverse transformation temperature of the remained martensite increases due to the constraint of the cement matrix. In the beginning of the reverse martensitic transformation, the average reverse transformation ratio is larger. Above the finish temperature of the endothermic peak in the DSC heating curve of the cement composite sample, the reverse transformation of the remained martensite is still undergoing slowly.
2002, 19(3): 70-74.
Abstract:
Ternary system piezoelectric ceramic materials PZN-PZT and their powders were fabricated using solid state sintered technology. Their structure and properties were studied by XRD and SEM. PZN-PZT ceramics synthesized by the traditional sintered method contain well piezoelectric properties. The diameters of PZN-PZT powders are between 0.5~4μm, and the shape is irregular. PZN-PZT particles were incorporated into PVDF polymer matrix homogeneously through solution blended process to form PZN-PZT/PVDF 0-3 composite thin films. The effects of the ceramic mass fraction and poling electric field on the piezoelectric and dielectric properties of the piezoelectric composites were studied. The results show that the piezoelectric properties of the composites could be improved effectively through choosing the ceramics containing better piezoelectric properties as the filler. The same effects can be made with the increasing of PZN-PZT mass fraction and poling field.
Ternary system piezoelectric ceramic materials PZN-PZT and their powders were fabricated using solid state sintered technology. Their structure and properties were studied by XRD and SEM. PZN-PZT ceramics synthesized by the traditional sintered method contain well piezoelectric properties. The diameters of PZN-PZT powders are between 0.5~4μm, and the shape is irregular. PZN-PZT particles were incorporated into PVDF polymer matrix homogeneously through solution blended process to form PZN-PZT/PVDF 0-3 composite thin films. The effects of the ceramic mass fraction and poling electric field on the piezoelectric and dielectric properties of the piezoelectric composites were studied. The results show that the piezoelectric properties of the composites could be improved effectively through choosing the ceramics containing better piezoelectric properties as the filler. The same effects can be made with the increasing of PZN-PZT mass fraction and poling field.
2002, 19(3): 75-82.
Abstract:
The fracture mechanics feature of elliptical delaminations in a composite laminate is studied. Using the method of normal slices, the relationship between stress intensity factors and energy release rate was established, based on the stress and displacement fields in the vicinity of the delamination-tip of a plane shear delamination and anti-plane shear delamination in a composite laminate. The distribution expression of the energy release rate along the front of the elliptical delamination area was obtained, combining with the total potential energy determined by the additional displacements. Computational results show the distribution of energy release rate and stress intensity factors with respect to the shape of delamination, load and thickness ratio of the laminate.
The fracture mechanics feature of elliptical delaminations in a composite laminate is studied. Using the method of normal slices, the relationship between stress intensity factors and energy release rate was established, based on the stress and displacement fields in the vicinity of the delamination-tip of a plane shear delamination and anti-plane shear delamination in a composite laminate. The distribution expression of the energy release rate along the front of the elliptical delamination area was obtained, combining with the total potential energy determined by the additional displacements. Computational results show the distribution of energy release rate and stress intensity factors with respect to the shape of delamination, load and thickness ratio of the laminate.
2002, 19(3): 83-87.
Abstract:
According to the analysis of the thermal chemical ablative mechanism of resin matrix materials under pyrolytic reaction at elevated temperature, the ablation-phase transformation properties and the thermal deformation behavior of the materials were investigated by Eshelby equivalent inclusion method. The interaction among different phases by thermal chemical reaction was considered using the hypothesis of the statistical uniform distribution for the pyrolytic phases (in the vacuum environment) in the materials. The thermal expansion coefficients of different resin matrix materials under different temperature and heating rates were predicted. The results are in good agreement with experimental data.
According to the analysis of the thermal chemical ablative mechanism of resin matrix materials under pyrolytic reaction at elevated temperature, the ablation-phase transformation properties and the thermal deformation behavior of the materials were investigated by Eshelby equivalent inclusion method. The interaction among different phases by thermal chemical reaction was considered using the hypothesis of the statistical uniform distribution for the pyrolytic phases (in the vacuum environment) in the materials. The thermal expansion coefficients of different resin matrix materials under different temperature and heating rates were predicted. The results are in good agreement with experimental data.
2002, 19(3): 88-93.
Abstract:
The divergence experiment prediction techniques of flat-plate forward-swept wings are presented. The Southwell method, a subcritical divergence experiment technique, was used for prediction of divergence dynamic pressure. By testing, some key techniques in the prediction experiment and critical experiment are introduced.In this experiment, three flat-plate forward-swept wings were tested, of which two are composite flat-plate wings and one is an aluminum flat-plate wing. In order to predict and validate the result of the subcritical experiment, the divergence dynamic pressures were calculated before experiment and the critical divergence wind-tunnel experiments are used. Both the calculating results and testing results indicate that better results can be attained by using the Southwell method. The divergence pressures of these models were calculated by the flexibility method of MSC/NASTRAN and the mode method developed by the authors, while the steady aerodynamics of the subsonic Doublet-Lattice method is used for aerodynamic calculation in both the methods. By making a comparison between the results of calculation, prediction experiment and critical experiment, it can be seen that all the three methods can make better results.
The divergence experiment prediction techniques of flat-plate forward-swept wings are presented. The Southwell method, a subcritical divergence experiment technique, was used for prediction of divergence dynamic pressure. By testing, some key techniques in the prediction experiment and critical experiment are introduced.In this experiment, three flat-plate forward-swept wings were tested, of which two are composite flat-plate wings and one is an aluminum flat-plate wing. In order to predict and validate the result of the subcritical experiment, the divergence dynamic pressures were calculated before experiment and the critical divergence wind-tunnel experiments are used. Both the calculating results and testing results indicate that better results can be attained by using the Southwell method. The divergence pressures of these models were calculated by the flexibility method of MSC/NASTRAN and the mode method developed by the authors, while the steady aerodynamics of the subsonic Doublet-Lattice method is used for aerodynamic calculation in both the methods. By making a comparison between the results of calculation, prediction experiment and critical experiment, it can be seen that all the three methods can make better results.
2002, 19(3): 94-97.
Abstract:
In this paper, an anisotropic design is introduced to the laminated damped plates. The damping analyses of laminated anisotropic damped plates were carried out theoretically. The results indicate that it is feasible to carry out the optimization design of laminated anisotropic damped plates for obtaining the maximum loss factor. An important index for evaluating the effect of reducing vibration is the loss factor of the structure system. Taking a semi-infinite plate as an example, a lot of composite structures were calculated by varying different layers and layer orientation angles. At the same time, after the loss factor was defined as the objective function, the optimization design was carried out for obtaining the maximum loss factor with constrained conditions as the layer angle, frequency and layer thickness. The numerical results show that the use of compliant inner layering appeared to have more of an effect on damping than stress coupling and in the higher than fundamental mode, and the compliant inner layering laminates have significantly greater loss factors.
In this paper, an anisotropic design is introduced to the laminated damped plates. The damping analyses of laminated anisotropic damped plates were carried out theoretically. The results indicate that it is feasible to carry out the optimization design of laminated anisotropic damped plates for obtaining the maximum loss factor. An important index for evaluating the effect of reducing vibration is the loss factor of the structure system. Taking a semi-infinite plate as an example, a lot of composite structures were calculated by varying different layers and layer orientation angles. At the same time, after the loss factor was defined as the objective function, the optimization design was carried out for obtaining the maximum loss factor with constrained conditions as the layer angle, frequency and layer thickness. The numerical results show that the use of compliant inner layering appeared to have more of an effect on damping than stress coupling and in the higher than fundamental mode, and the compliant inner layering laminates have significantly greater loss factors.
2002, 19(3): 98-104.
Abstract:
Film/substrate structure is a basic structure widely used in microelectronic and materials science and technology. The residual stress in the film induced by mechanical and thermal mismatch in the manufacture is an important cause of initiation and extension of interface cracks. The modified three-parameter (Γ0, /σy,t) cohesive model was used to investigate the cleavage fracture under plastic atmosphere, the stress distribution in crack tip, the shape and physiognomy of crack tip and the influence of the parameter on the fracture process. The model was also used to discuss the whole process of the initiation and extension of an interface crack between a uniform metal thin film and a ceramic substrate under residual stresses.
Film/substrate structure is a basic structure widely used in microelectronic and materials science and technology. The residual stress in the film induced by mechanical and thermal mismatch in the manufacture is an important cause of initiation and extension of interface cracks. The modified three-parameter (Γ0, /σy,t) cohesive model was used to investigate the cleavage fracture under plastic atmosphere, the stress distribution in crack tip, the shape and physiognomy of crack tip and the influence of the parameter on the fracture process. The model was also used to discuss the whole process of the initiation and extension of an interface crack between a uniform metal thin film and a ceramic substrate under residual stresses.
2002, 19(3): 106-109.
Abstract:
The numerical method of the elastic wave guide problem of composite materials is studied. The wave guide problem was introduced to a Hamiltonian system. In the Hamiltonian system, the displacement vectors and stress vectors were combined to be the whole state vectors, and the system was a hybrid system. In the hybrid system, the dynamic hybrid element was deduced, and a new semi-analysis finite element method in the Hamiltonian system was founded. This method is given in detail through the solution of layered media wave guide problems in a strip domain and its broad prospect is embodied.
The numerical method of the elastic wave guide problem of composite materials is studied. The wave guide problem was introduced to a Hamiltonian system. In the Hamiltonian system, the displacement vectors and stress vectors were combined to be the whole state vectors, and the system was a hybrid system. In the hybrid system, the dynamic hybrid element was deduced, and a new semi-analysis finite element method in the Hamiltonian system was founded. This method is given in detail through the solution of layered media wave guide problems in a strip domain and its broad prospect is embodied.
2002, 19(3): 109-113.
Abstract:
A genetic algorithm(Pareto GA), based on a sharing niche technique, is applied to search a Pareto optimal set in a multiobjective optimization problem. On the basis of considering synthetically the belt durability and tire weight, a mathematical model was founded by a three-dimensional finite element analysis and indoor durability test. The mathematical model was calculated by means of Pareto GA, and the Pareto optimal set, which was dispersed well, was attained. In order to evaluate the result of optimization, the tire with the optimized belt structure was analyzed by the three-dimensional finite element analysis technology, and the analysis result was compared with that of the original tire. The result shows that the goal of optimization is achieved.
A genetic algorithm(Pareto GA), based on a sharing niche technique, is applied to search a Pareto optimal set in a multiobjective optimization problem. On the basis of considering synthetically the belt durability and tire weight, a mathematical model was founded by a three-dimensional finite element analysis and indoor durability test. The mathematical model was calculated by means of Pareto GA, and the Pareto optimal set, which was dispersed well, was attained. In order to evaluate the result of optimization, the tire with the optimized belt structure was analyzed by the three-dimensional finite element analysis technology, and the analysis result was compared with that of the original tire. The result shows that the goal of optimization is achieved.
2002, 19(3): 114-119.
Abstract:
Based on the linear visco-elasticity theory, a variational mathematical model was developed using Hamilton's principle to describe the dynamics of ER sandwich beams. And a modal analysis of ER beam, considering simple boundary conditions, was performed. Some conclusions are drawn: the modal frequency and modal loss factor of the ER beam will become bigger when the applied electric field intensity is increased.
Based on the linear visco-elasticity theory, a variational mathematical model was developed using Hamilton's principle to describe the dynamics of ER sandwich beams. And a modal analysis of ER beam, considering simple boundary conditions, was performed. Some conclusions are drawn: the modal frequency and modal loss factor of the ER beam will become bigger when the applied electric field intensity is increased.
2002, 19(3): 120-123.
Abstract:
Within the field of fiber, paper making, plastic and metal plating, one of the key techniques to guarantee the product quality is the control of winding tension of linear, strip and area materials. The changing pattern of the tension and the factors that influence the tension in the process of filament winding were analyzed, and a program scheme for calculating the tension control torque was provided. The actual winding results show that the formula drawn is proper and reasonable, and the fluctuation rate of the yarn tension is lower than 5%.
Within the field of fiber, paper making, plastic and metal plating, one of the key techniques to guarantee the product quality is the control of winding tension of linear, strip and area materials. The changing pattern of the tension and the factors that influence the tension in the process of filament winding were analyzed, and a program scheme for calculating the tension control torque was provided. The actual winding results show that the formula drawn is proper and reasonable, and the fluctuation rate of the yarn tension is lower than 5%.
2002, 19(3): 124-126.
Abstract:
The thermal expansion coefficients of fiber composites are studied in this paper. A method of measuring the thermal expansion coefficient by piezoelectric photoacoustic technique was proposed. An intensity-modulated Ar+ laser beam was used as the incident light. The beam was focused on an about 1μm diameter spot and illuminated collinearly the sample surface. Using the technique, piezoelectric photoacoustic signals as a function of different frequencies were experimentally measured. The thermal expansion coefficients can be obtained by fitting the experimental data. On the other hand, the thermal expansion coefficients of one-way composite C/C and C/Al in the transverse, longitudinal directions were measured. The measured results are reliable by comparing with other calculation methods and experimental results. Thermal expansion coefficients in arbitrary directions of C/C and C/A were given. The defects of the theoretical calculation method, which is complicated and by which the thermal expansion coefficient in arbitrary directions can not be measured, are overcome.
The thermal expansion coefficients of fiber composites are studied in this paper. A method of measuring the thermal expansion coefficient by piezoelectric photoacoustic technique was proposed. An intensity-modulated Ar+ laser beam was used as the incident light. The beam was focused on an about 1μm diameter spot and illuminated collinearly the sample surface. Using the technique, piezoelectric photoacoustic signals as a function of different frequencies were experimentally measured. The thermal expansion coefficients can be obtained by fitting the experimental data. On the other hand, the thermal expansion coefficients of one-way composite C/C and C/Al in the transverse, longitudinal directions were measured. The measured results are reliable by comparing with other calculation methods and experimental results. Thermal expansion coefficients in arbitrary directions of C/C and C/A were given. The defects of the theoretical calculation method, which is complicated and by which the thermal expansion coefficient in arbitrary directions can not be measured, are overcome.
