2002 Vol. 19, No. 2
2002, 19(2): 1-12.
Abstract:
Composite materials have been widely applied because of their many desirable properties. But the bottleneck to widespread acceptance in more commonplace applications is the inability to manufacture composite parts cheaply and reliably. The cure cycle has a significant effect on the quality of the finished part.The traditional cure cycle based on an empirical approach could not ensure the quality of cured products in the aspects of unstabilized performance, the high cost of production and the low efficiency. In this paper, the technology of intelligent cure operation is set forth according to the developing tendency of smart material and structure. An intelligent-system-based tool was developed in order to operate the autoclave cure of a fiber reinforced thermosetting matrix composite laminate in an optimal manner. The intelligent system includes an expert system, a neural network and the step optimal model whose function,structure and attaching parts are systematically set forth. They can achieve the desired objectives such as minimizing the cure time while still producing a high quality part.
Composite materials have been widely applied because of their many desirable properties. But the bottleneck to widespread acceptance in more commonplace applications is the inability to manufacture composite parts cheaply and reliably. The cure cycle has a significant effect on the quality of the finished part.The traditional cure cycle based on an empirical approach could not ensure the quality of cured products in the aspects of unstabilized performance, the high cost of production and the low efficiency. In this paper, the technology of intelligent cure operation is set forth according to the developing tendency of smart material and structure. An intelligent-system-based tool was developed in order to operate the autoclave cure of a fiber reinforced thermosetting matrix composite laminate in an optimal manner. The intelligent system includes an expert system, a neural network and the step optimal model whose function,structure and attaching parts are systematically set forth. They can achieve the desired objectives such as minimizing the cure time while still producing a high quality part.
2002, 19(2): 13-17.
Abstract:
Resin Transfer Molding is one of the most common fabrication methods for composite materials. It is attractive for high performance and low cost manufacturing of polymer composites. In this paper, the Control Volume Finite Element Method (CVFEM) was applied to simulate RTM mold filling. The computational formulas of triangular and quadrangular elements were presented for details. Some case studies were conducted. The results showed that the quadrangular element has higher computational performance than the triangular element and can be used with the triangular elements.
Resin Transfer Molding is one of the most common fabrication methods for composite materials. It is attractive for high performance and low cost manufacturing of polymer composites. In this paper, the Control Volume Finite Element Method (CVFEM) was applied to simulate RTM mold filling. The computational formulas of triangular and quadrangular elements were presented for details. Some case studies were conducted. The results showed that the quadrangular element has higher computational performance than the triangular element and can be used with the triangular elements.
2002, 19(2): 18-23.
Abstract:
Numerical simulation of resin transfer molding is important to mold design, process control and parameter optimization. This paper introduces the RTM process and its characterizations briefly. The governing equations of resin flow are presented. Based on the exposition of main problems of the commonly used methods in modeling the RTM process, the boundary-fitted coordinate system and the finite difference method as well as the resin flow domain decomposition process are employed to simulate the RTM resin flow process in the case of mold with interior insert. The successive resin flow front position,calculating mesh and the pressure distribution at the final stage are obtained, which is helpful for locating the air vent, and good agreement is found between the results and other investigations. The results indicate that the method provided by this paper is convenient and effective in solving the moving boundary problems with irregularly geometric boundaries.
Numerical simulation of resin transfer molding is important to mold design, process control and parameter optimization. This paper introduces the RTM process and its characterizations briefly. The governing equations of resin flow are presented. Based on the exposition of main problems of the commonly used methods in modeling the RTM process, the boundary-fitted coordinate system and the finite difference method as well as the resin flow domain decomposition process are employed to simulate the RTM resin flow process in the case of mold with interior insert. The successive resin flow front position,calculating mesh and the pressure distribution at the final stage are obtained, which is helpful for locating the air vent, and good agreement is found between the results and other investigations. The results indicate that the method provided by this paper is convenient and effective in solving the moving boundary problems with irregularly geometric boundaries.
2002, 19(2): 24-27.
Abstract:
A toughened epoxy resin matrix is designed for the wet-winding of a carbon fiber composite solid rocket motor case, under the consideration of the relations among viscosity, mechanical and heat-resistance properties.The curing kinetic parameter, gel time and properties of casting parts and carbon fiber composite are studied by means of DSC, FT-IR, ect. The results showed that the formulation of the toughened epoxy resin matrix has low viscosity, longer-life-time and higher toughness, the matrix has strong interfacial adhesion with the carbon fiber, and the strength conversion ratio of the carbon fiber is high.
A toughened epoxy resin matrix is designed for the wet-winding of a carbon fiber composite solid rocket motor case, under the consideration of the relations among viscosity, mechanical and heat-resistance properties.The curing kinetic parameter, gel time and properties of casting parts and carbon fiber composite are studied by means of DSC, FT-IR, ect. The results showed that the formulation of the toughened epoxy resin matrix has low viscosity, longer-life-time and higher toughness, the matrix has strong interfacial adhesion with the carbon fiber, and the strength conversion ratio of the carbon fiber is high.
2002, 19(2): 28-32.
Abstract:
A type of LTM resin system, which can be cured at low temperatures but is high temperature resistant, Xufyg series was formulated in this work, whose heat properties,curing degree and Tg varying with storage time at room temperature and curing time at 60℃ were reported by using DSC and DMTA.According to the result,Xufyg-44 is selected as representative.Then the curing processing of Xufyg-44 is decided by DMTA scanning. When it is used for manufacturing composite articles, the curing temperature can be lower than 70℃, while the final cured product has a glass transition temperature higher than 200℃. The mechanical properties of the resin casts and the dimension stability of composite articles during curing and post curing are found well.
A type of LTM resin system, which can be cured at low temperatures but is high temperature resistant, Xufyg series was formulated in this work, whose heat properties,curing degree and Tg varying with storage time at room temperature and curing time at 60℃ were reported by using DSC and DMTA.According to the result,Xufyg-44 is selected as representative.Then the curing processing of Xufyg-44 is decided by DMTA scanning. When it is used for manufacturing composite articles, the curing temperature can be lower than 70℃, while the final cured product has a glass transition temperature higher than 200℃. The mechanical properties of the resin casts and the dimension stability of composite articles during curing and post curing are found well.
2002, 19(2): 33-36.
Abstract:
Along with the increase in the time of high-energy ball milling, the grain size of Al-Ti-C powder mixture is decreased continuously and the distribution uniformity of each element in the mixture is improved obviously. Meanwhile, the powders are aggregated with each other. In addition, the crystal size within each powder particle is also decreased during ball milling, while the defects in the crystal are increased. After milling for a certain time, the nano-crystals are formed. Going a step further, the amorphous structure will be also produced. These factors are beneficial to diffusion and promote the completion of the synthesis reactions.
Along with the increase in the time of high-energy ball milling, the grain size of Al-Ti-C powder mixture is decreased continuously and the distribution uniformity of each element in the mixture is improved obviously. Meanwhile, the powders are aggregated with each other. In addition, the crystal size within each powder particle is also decreased during ball milling, while the defects in the crystal are increased. After milling for a certain time, the nano-crystals are formed. Going a step further, the amorphous structure will be also produced. These factors are beneficial to diffusion and promote the completion of the synthesis reactions.
2002, 19(2): 37-40.
Abstract:
A new kind of flier-plate material with graded density has come to show great potential for the application in dynamic high-pressure technology. In the present paper, W-Mo-Ti system was chosen to prepare such graded density flier-plate materials. It is found that the Fe-Al additives were suitable for the hot-pressing of W alloy, W-Mo alloys and Mo-Ti alloys at a low temperature of 1473 K. The mechanism of the densification could be expressed as follows: Part of Fe powders dissolved into the liquid due to the addition of Al and thus displayed more active feature during the sintering, which promoted the formation of bonding-phase in W-Mo alloys and solid solution in Mo-Ti alloys, and evidently improved their relative densities. Finally, a wholly dense W-Mo-Ti graded density flier-plate material was successfully fabricated. Its density changed gradually from 4.5×103 kg/m3 up to 17.0×103 kg/m3.
A new kind of flier-plate material with graded density has come to show great potential for the application in dynamic high-pressure technology. In the present paper, W-Mo-Ti system was chosen to prepare such graded density flier-plate materials. It is found that the Fe-Al additives were suitable for the hot-pressing of W alloy, W-Mo alloys and Mo-Ti alloys at a low temperature of 1473 K. The mechanism of the densification could be expressed as follows: Part of Fe powders dissolved into the liquid due to the addition of Al and thus displayed more active feature during the sintering, which promoted the formation of bonding-phase in W-Mo alloys and solid solution in Mo-Ti alloys, and evidently improved their relative densities. Finally, a wholly dense W-Mo-Ti graded density flier-plate material was successfully fabricated. Its density changed gradually from 4.5×103 kg/m3 up to 17.0×103 kg/m3.
2002, 19(2): 41-44.
Abstract:
The hardening properties of carbide (WC)-reinforced steel matrix composites after austenization between 980℃~1240℃ have been investigated. It has been found that the tested material has a remarkable hardening effect, 68HRC, and tempering resistance.The present work has measured the micro-hardness (HV0.05) of the massive hard phase, WC aggregated and matrix in the material microstructures and studied the relationship between the micro-hardness (HV0.05) and macro-hardness(HRC). From materialogy and alloy electron theory, the highly hardening effect comes from the contributions of the strong martensite matrix containing carbon structure units with W, Mo, etc and numerous hard phases.
The hardening properties of carbide (WC)-reinforced steel matrix composites after austenization between 980℃~1240℃ have been investigated. It has been found that the tested material has a remarkable hardening effect, 68HRC, and tempering resistance.The present work has measured the micro-hardness (HV0.05) of the massive hard phase, WC aggregated and matrix in the material microstructures and studied the relationship between the micro-hardness (HV0.05) and macro-hardness(HRC). From materialogy and alloy electron theory, the highly hardening effect comes from the contributions of the strong martensite matrix containing carbon structure units with W, Mo, etc and numerous hard phases.
2002, 19(2): 45-48.
Abstract:
Ti-54Al-xB alloys have been produced by an in-situ method. The microstructure and phases constituent of these alloys were investigated by XRD and SEM. The results show that there are needle shape dendrites which are parallel to [0001] on the edge of TiB2 plate and convex flakes which are perpendicular to [0001]on the surface of TiB2 plate. These needles or flakes exhibit facets parallel to those of TiB2 plate. It was analyzed that the Al rich layer and inhomogeneity in supersaturation at the solid-liquid interface resulting from non-equilibrium solidification may make the solid-liquid interface unstable, and lead TiB2 plate to forming the surface structure.
Ti-54Al-xB alloys have been produced by an in-situ method. The microstructure and phases constituent of these alloys were investigated by XRD and SEM. The results show that there are needle shape dendrites which are parallel to [0001] on the edge of TiB2 plate and convex flakes which are perpendicular to [0001]on the surface of TiB2 plate. These needles or flakes exhibit facets parallel to those of TiB2 plate. It was analyzed that the Al rich layer and inhomogeneity in supersaturation at the solid-liquid interface resulting from non-equilibrium solidification may make the solid-liquid interface unstable, and lead TiB2 plate to forming the surface structure.
2002, 19(2): 49-53.
Abstract:
Cement-based material is an inert material with high electrical resistivity, but its electrical conductivity can be obviously improved by the addition of short carbon fibers (0.2 vol%~ 1.2 vol%). In this paper, the relationships between inner microstructure and apparent electrical properties, change of electrical resistivity and external applied load of carbon fiber reinforced cement-based material were investigated. The test results indicated that the carbon fiber reinforced cement-based material could function as a smart material for the real time diagnosis of damage. The electrical signal is related to an increase in the material's volume resistivity during the crack generation or propagation and a decrease in the resistivity during crack closure. The linearity between the electrical resistance change and the applied load was good for the carbon fiber reinforced cement-based material. In contrast, the cement-based material without carbon fibers showed no variation of the resistivity during the entire load process. The change of electrical characteristics reflects large numbers of information of inner damage of the cement-based material, which can be used to detect potential damage and to prevent fatal failure.
Cement-based material is an inert material with high electrical resistivity, but its electrical conductivity can be obviously improved by the addition of short carbon fibers (0.2 vol%~ 1.2 vol%). In this paper, the relationships between inner microstructure and apparent electrical properties, change of electrical resistivity and external applied load of carbon fiber reinforced cement-based material were investigated. The test results indicated that the carbon fiber reinforced cement-based material could function as a smart material for the real time diagnosis of damage. The electrical signal is related to an increase in the material's volume resistivity during the crack generation or propagation and a decrease in the resistivity during crack closure. The linearity between the electrical resistance change and the applied load was good for the carbon fiber reinforced cement-based material. In contrast, the cement-based material without carbon fibers showed no variation of the resistivity during the entire load process. The change of electrical characteristics reflects large numbers of information of inner damage of the cement-based material, which can be used to detect potential damage and to prevent fatal failure.
2002, 19(2): 54-58.
Abstract:
A new type of organic-inorganic hybrid material,made of carboxyl methyl starch and titanium dioxide, is synthesized by means of modified in-situ sol-gel technique. IR analysis shows that there is somewhat weak interaction between these two components,whose dispersion is almost up to a molecular level. A series of physical properties of suspension of this hybrid in methyl silicone oil are investigated under direct current field. The mechanic performance of this hybrid ERF is much stronger than that of pure starch, titanium oxide and their blends ERF. For example, the static shear stress is above 4 kPa, shear rate 5 s-1,when 4 kV/mm DC is applied at room temperature. In the meanwhile, the temperature effect is optimized; its maximum stress appears at around 70 ℃, and remains a considerable value at even 90 ℃. In addition, by adjusting the displacement ratio of carboxyl in starch, its suspension stability can be much improved.
A new type of organic-inorganic hybrid material,made of carboxyl methyl starch and titanium dioxide, is synthesized by means of modified in-situ sol-gel technique. IR analysis shows that there is somewhat weak interaction between these two components,whose dispersion is almost up to a molecular level. A series of physical properties of suspension of this hybrid in methyl silicone oil are investigated under direct current field. The mechanic performance of this hybrid ERF is much stronger than that of pure starch, titanium oxide and their blends ERF. For example, the static shear stress is above 4 kPa, shear rate 5 s-1,when 4 kV/mm DC is applied at room temperature. In the meanwhile, the temperature effect is optimized; its maximum stress appears at around 70 ℃, and remains a considerable value at even 90 ℃. In addition, by adjusting the displacement ratio of carboxyl in starch, its suspension stability can be much improved.
2002, 19(2): 59-64.
Abstract:
Nanoparticles gelatin-iron oxides composite particles have been prepared with the microemulsion method.The investigations by XRD,SEM, TEM and IR show the ultrafine particles are spheroids coated by gelatin.Their average sizes are 1.5μm~3μm, and particles sizes are 20 nm,about 35~90 iron-oxides particles on each spheroid.The specific saturation magnetization σs=62Am2/kg,the coercivity Hc=187Oe and residual magnetism r=10.18 Am2/kg for the composite particles. The coercivity and residual magnetism are higher, and it is shown that the complex supermicropower has hard magnetic properties. Magneticrheological (MR) effects of the MR fluid prepared from the ultrafine particles are superior in lower magnetic field intensity and the subsidence stability of the MRF is excellent compared with carbonyl iron powder.
Nanoparticles gelatin-iron oxides composite particles have been prepared with the microemulsion method.The investigations by XRD,SEM, TEM and IR show the ultrafine particles are spheroids coated by gelatin.Their average sizes are 1.5μm~3μm, and particles sizes are 20 nm,about 35~90 iron-oxides particles on each spheroid.The specific saturation magnetization σs=62Am2/kg,the coercivity Hc=187Oe and residual magnetism r=10.18 Am2/kg for the composite particles. The coercivity and residual magnetism are higher, and it is shown that the complex supermicropower has hard magnetic properties. Magneticrheological (MR) effects of the MR fluid prepared from the ultrafine particles are superior in lower magnetic field intensity and the subsidence stability of the MRF is excellent compared with carbonyl iron powder.
2002, 19(2): 65-70.
Abstract:
The microwave absorbing property of nano Si/C/N composite powder has been studied in the frequency range of 8.2 GHz~18 GHz. The nano Si/C/N composite powder with its size in the range of 20 nm~30 nm was synthesized from hexamethyldisilazane ((Me3Si)2NH) (Me:CH3) by a laser-induced gas-phase reaction. The dissipation factors of the nano Si/C/N composite powder were high at the microwave frequencies. The microwave permittivity of the mixtures of nano Si/C/N composite powder and paraffin wax or epoxy resin can be tailored by the content of this composite powder. The unusual ε',ε″ and dissipation factor tgδ(ε″/ε') of the nano Si/C/N composite powder suspended in different matrixes were attributed to the interface effects between the nano Si/C/N composite powder and matrix. The ε' and ε″ of the nano Si/C/N composite powder decreased with frequency in the frequency range of 8.2 GHz~18 GHz. The difference being that the microwave resonance was not sharply peaked but rather smeared out over a large frequency range. The promising features of nano Si/C/N composite powder would be due to the more complicated Si, C and N atomic chemical environment than in a mixture of pure SiC and Si3N4 phase. So charged defects and quasi-free electrons moved in response to the electric field, diffusion or polarization current resulted from the field propagation. The high ε″ and tgδ of nano Si/C/N composite powder were due to the dielectric relaxation. The nano Si/C/N composite powder would be a good candidate for microwave absorbing materials. The microwave absorbing coating structure was designed on the basis of measured ε' and ε″ of the composites composed of nano Si/C/N powders and paraffin wax. Several three-layer microwave absorbing coatings with the reflection coefficient less than -8dB in the frequency range of 8 GHz~18 GHz were designed with depth of three millimeters.
The microwave absorbing property of nano Si/C/N composite powder has been studied in the frequency range of 8.2 GHz~18 GHz. The nano Si/C/N composite powder with its size in the range of 20 nm~30 nm was synthesized from hexamethyldisilazane ((Me3Si)2NH) (Me:CH3) by a laser-induced gas-phase reaction. The dissipation factors of the nano Si/C/N composite powder were high at the microwave frequencies. The microwave permittivity of the mixtures of nano Si/C/N composite powder and paraffin wax or epoxy resin can be tailored by the content of this composite powder. The unusual ε',ε″ and dissipation factor tgδ(ε″/ε') of the nano Si/C/N composite powder suspended in different matrixes were attributed to the interface effects between the nano Si/C/N composite powder and matrix. The ε' and ε″ of the nano Si/C/N composite powder decreased with frequency in the frequency range of 8.2 GHz~18 GHz. The difference being that the microwave resonance was not sharply peaked but rather smeared out over a large frequency range. The promising features of nano Si/C/N composite powder would be due to the more complicated Si, C and N atomic chemical environment than in a mixture of pure SiC and Si3N4 phase. So charged defects and quasi-free electrons moved in response to the electric field, diffusion or polarization current resulted from the field propagation. The high ε″ and tgδ of nano Si/C/N composite powder were due to the dielectric relaxation. The nano Si/C/N composite powder would be a good candidate for microwave absorbing materials. The microwave absorbing coating structure was designed on the basis of measured ε' and ε″ of the composites composed of nano Si/C/N powders and paraffin wax. Several three-layer microwave absorbing coatings with the reflection coefficient less than -8dB in the frequency range of 8 GHz~18 GHz were designed with depth of three millimeters.
2002, 19(2): 71-74.
Abstract:
In the braiding procedure, all of yarns are interwoven by the intermittent movement of carriers. The braiding yarn is tended to move along the direction of the carrier movement. In this paper, a method of least square approximation was introduced to predict the trend line of carrier movement. Then the yarn paths were analyzed systematically. Finally, two kinds of unit cells, the interior cell and the surface cell, were established. They are oriented in the same reference frame as the preform, which is quite suitable for the analysis of the mechanical properties.
In the braiding procedure, all of yarns are interwoven by the intermittent movement of carriers. The braiding yarn is tended to move along the direction of the carrier movement. In this paper, a method of least square approximation was introduced to predict the trend line of carrier movement. Then the yarn paths were analyzed systematically. Finally, two kinds of unit cells, the interior cell and the surface cell, were established. They are oriented in the same reference frame as the preform, which is quite suitable for the analysis of the mechanical properties.
2002, 19(2): 75-79.
Abstract:
Axial crushing energy dissipation behavior of glass/epoxy round tubes is investigated both dynamically and quasi-statically. Three macroscopic collapse modes are observed and summarized during the stable crushing process: they are lamina bending, local buckling and transverse shearing. From the view-point of microscopic mechanism, energy dissipation mechanisms are studied for different macro collapse modes, and their energy absorption capabilities are compared in details. As the winding angle increased, energy absorption efficiency of the composite tube is improved, because the controlling energy dissipation mechanism is changing from matrix fracture to fiber/matrix fracture. Energy absorption characteristics are also compared between the impact test and quasi-static test; for tubes of 5 and 5, energy absorption capability in the impact test is higher than that in quasi-static loading, whereas for tubes with the plying angle greater than 45°, the situation is opposite.
Axial crushing energy dissipation behavior of glass/epoxy round tubes is investigated both dynamically and quasi-statically. Three macroscopic collapse modes are observed and summarized during the stable crushing process: they are lamina bending, local buckling and transverse shearing. From the view-point of microscopic mechanism, energy dissipation mechanisms are studied for different macro collapse modes, and their energy absorption capabilities are compared in details. As the winding angle increased, energy absorption efficiency of the composite tube is improved, because the controlling energy dissipation mechanism is changing from matrix fracture to fiber/matrix fracture. Energy absorption characteristics are also compared between the impact test and quasi-static test; for tubes of 5 and 5, energy absorption capability in the impact test is higher than that in quasi-static loading, whereas for tubes with the plying angle greater than 45°, the situation is opposite.
2002, 19(2): 80-84.
Abstract:
Based on the zig-zag deformation model and first order shear strain effect laminated plate theory, a nonlinear buckling finite-element method of the composite sandwich plates is proposed, which contains both interfacial delamination and matrix micro-cracks damages. Furthermore, the transverse shear properties of the faces and the in-plane stiffness of the core are also taken into account. Furthermore, a delamination model and a multi-scalar damage model have been established, respectively. Because of the material properties of the face being degraded with the matrix micro-cracks propagation, the incremental constitutive equations are derived, and a modified Newton-Raphson incremental-iterative method is employed during the numerical calculation procedure. According to the models and analysis method provided by the authors, a nonlinear finite-element code has been developed. Some numerical examples are given for investigation of the effect of sizes of delamination and matrix micro-cracks, ply angles of the faces, and load cases upon the buckling behavior of the damaged composite sandwich plates. The numerical method and conclusions would be useful for the engineers of sandwich composite structures.
Based on the zig-zag deformation model and first order shear strain effect laminated plate theory, a nonlinear buckling finite-element method of the composite sandwich plates is proposed, which contains both interfacial delamination and matrix micro-cracks damages. Furthermore, the transverse shear properties of the faces and the in-plane stiffness of the core are also taken into account. Furthermore, a delamination model and a multi-scalar damage model have been established, respectively. Because of the material properties of the face being degraded with the matrix micro-cracks propagation, the incremental constitutive equations are derived, and a modified Newton-Raphson incremental-iterative method is employed during the numerical calculation procedure. According to the models and analysis method provided by the authors, a nonlinear finite-element code has been developed. Some numerical examples are given for investigation of the effect of sizes of delamination and matrix micro-cracks, ply angles of the faces, and load cases upon the buckling behavior of the damaged composite sandwich plates. The numerical method and conclusions would be useful for the engineers of sandwich composite structures.
2002, 19(2): 85-88.
Abstract:
The damping properties of a SMA hybrid composite lamina with fibers reinforced unidirectionally are investigated by using a simplified micromechanic damping theory. The analytical equations corresponding to all the six in plane and out-of-plane damping parameters are presented. Numerical studies are carried out to demonstrate the damping enhancement of hybridization effect by embedding NiTi fibers.
The damping properties of a SMA hybrid composite lamina with fibers reinforced unidirectionally are investigated by using a simplified micromechanic damping theory. The analytical equations corresponding to all the six in plane and out-of-plane damping parameters are presented. Numerical studies are carried out to demonstrate the damping enhancement of hybridization effect by embedding NiTi fibers.
2002, 19(2): 89-93.
Abstract:
An increment shape memory alloy (SMA) constitutive relation is developed based on the SMA constitutive model produced by the authors; a new micromechanical constitutive model of composite reinforced by long SMA is constructed by using the relations of micromechanics; mechanical properties of the composite are investigated by using the new model, and some quantitative conclusions, especially the variation of stress in the constitution, are given, which is helpful to design the intelligent composites.
An increment shape memory alloy (SMA) constitutive relation is developed based on the SMA constitutive model produced by the authors; a new micromechanical constitutive model of composite reinforced by long SMA is constructed by using the relations of micromechanics; mechanical properties of the composite are investigated by using the new model, and some quantitative conclusions, especially the variation of stress in the constitution, are given, which is helpful to design the intelligent composites.
2002, 19(2): 94-98.
Abstract:
The nonlinear dynamic properties of a shape-memory-alloy-reinforced system for the purpose of vibration suppression are studied. The shape-memory-alloy-reinforced structure is simplified to a single-degree-of-freedom system by using the constitutive and internal friction models proposed by Brinson and Dejonghe, respectively. The internal friction is then expressed as the damping ratio of the shape memory alloy. In the case of weak nonlinear vibrations, the analytical solution of free vibration of the simplified system by using a small parameter method is obtained, while the weak nonlinear responses of the system excited by a simple harmonic force and forces in more generalized forms are proposed as well. The paper also presents an iterative algorithm for solving the system in a stronger nonlinear case. In this case, the total load history is divided into steps at which changes of stiffness and damping of the shape memory alloy reinforcement caused by martensite transformation and its inverse are taken into account. For each step, the problem is formulated as a weak nonlinear one and then solved by the aforementioned approach. Three examples of free and forced vibrations are provided. The results show that shape memory alloy reinforcement can be used as an efficient component in passive vibration control.
The nonlinear dynamic properties of a shape-memory-alloy-reinforced system for the purpose of vibration suppression are studied. The shape-memory-alloy-reinforced structure is simplified to a single-degree-of-freedom system by using the constitutive and internal friction models proposed by Brinson and Dejonghe, respectively. The internal friction is then expressed as the damping ratio of the shape memory alloy. In the case of weak nonlinear vibrations, the analytical solution of free vibration of the simplified system by using a small parameter method is obtained, while the weak nonlinear responses of the system excited by a simple harmonic force and forces in more generalized forms are proposed as well. The paper also presents an iterative algorithm for solving the system in a stronger nonlinear case. In this case, the total load history is divided into steps at which changes of stiffness and damping of the shape memory alloy reinforcement caused by martensite transformation and its inverse are taken into account. For each step, the problem is formulated as a weak nonlinear one and then solved by the aforementioned approach. Three examples of free and forced vibrations are provided. The results show that shape memory alloy reinforcement can be used as an efficient component in passive vibration control.
2002, 19(2): 99-102.
Abstract:
Conventional ply composites have shortcomings such as low interlaminar strength, which limit their application in the field of aeronautics and astronautics. Braided composites can overcome those limitations. Having good strength and antifatigue performances, carbon hermetically coated optic fibers have been used in benthal optic cables, military guiding optic fibers and optic fiber sensing systems under harsh circumstances. In this paper, the application of carbon hermetically coated optic fibers in braided carbon/epoxy composites is studied through experiments. The optic fibers are successfully braided into 3-D braided composite testpieces and processed through Resin Transfer Molding. Optic performance parameters of the optic fibers before, after their being braided into the testpieces, and after the molding process are tested, and compared. The results show that those parameters nearly do not change. Polarimetric optic fiber sensors using carbon hermetically coated optic fibers are designed for measuring the internal strain in braided testpieces under bending loads.
Conventional ply composites have shortcomings such as low interlaminar strength, which limit their application in the field of aeronautics and astronautics. Braided composites can overcome those limitations. Having good strength and antifatigue performances, carbon hermetically coated optic fibers have been used in benthal optic cables, military guiding optic fibers and optic fiber sensing systems under harsh circumstances. In this paper, the application of carbon hermetically coated optic fibers in braided carbon/epoxy composites is studied through experiments. The optic fibers are successfully braided into 3-D braided composite testpieces and processed through Resin Transfer Molding. Optic performance parameters of the optic fibers before, after their being braided into the testpieces, and after the molding process are tested, and compared. The results show that those parameters nearly do not change. Polarimetric optic fiber sensors using carbon hermetically coated optic fibers are designed for measuring the internal strain in braided testpieces under bending loads.
2002, 19(2): 103-107.
Abstract:
By using unidirectional cord reinforced rubber composites, the effect of generation heat on the fatigue behavior of rubber composites under cyclic loading was assessed. A great amount of heat was generated during the fatigue process of rubber composites. SEM photomicrographs show that the fracture surface of rubber composites under cyclic loading is closely interrelated with the generation heat. The energy loss which does not convert to effective heat generation is associated with fatigue damage in relation to the structural change leading to fatigue failure. It is found out that a quantitative relation exists between the average effective energy loss of fatigue damage and the fatigue life of rubber composites.
By using unidirectional cord reinforced rubber composites, the effect of generation heat on the fatigue behavior of rubber composites under cyclic loading was assessed. A great amount of heat was generated during the fatigue process of rubber composites. SEM photomicrographs show that the fracture surface of rubber composites under cyclic loading is closely interrelated with the generation heat. The energy loss which does not convert to effective heat generation is associated with fatigue damage in relation to the structural change leading to fatigue failure. It is found out that a quantitative relation exists between the average effective energy loss of fatigue damage and the fatigue life of rubber composites.
2002, 19(2): 108-112.
Abstract:
According to the analysis of the volume ablative mechanism of thermal protective materials under elevated temperatures, the ablation-phase transformation properties and the thermomechanical behavior of the materials are investigated by Eshelby equivalent inclusion method. The interaction among different phases by thermal chemical reaction is considered using the hypothesis of the statistical uniform distribution for the pyrolytic phases (in the vacuum environment) in the materials. The elastic moduli of different matrix materials under different temperatures and heating rates are predicted. The results are in good agreement with experimental data.
According to the analysis of the volume ablative mechanism of thermal protective materials under elevated temperatures, the ablation-phase transformation properties and the thermomechanical behavior of the materials are investigated by Eshelby equivalent inclusion method. The interaction among different phases by thermal chemical reaction is considered using the hypothesis of the statistical uniform distribution for the pyrolytic phases (in the vacuum environment) in the materials. The elastic moduli of different matrix materials under different temperatures and heating rates are predicted. The results are in good agreement with experimental data.
