The solidification microstructures and micro-segregation of a fiber reinforced Al-9 Cu alloy, containing different volume fractions of Al2O3 short fibers about 6μm diameter and made by squeeze casting have been studi...The solidification microstructures and micro-segregation of a fiber reinforced Al-9 Cu alloy, containing different volume fractions of Al2O3 short fibers about 6μm diameter and made by squeeze casting have been studied. The results indicate that as volume fraction of fiber Vf. increases, the size of final grains becomes finer in the matrix. If λf 〉λ〉1, the fibers have almost no influence on the solidification behavior of the matrix, so the final grains grow coarse, where λf is the average inter-fiber spacing and A is the secondary dendrite arm spacing. While if λf/ 〈λ〈1, the growth of crystals in the matrix is affected significantly by the fibers and the grain size is reduced to the value of the inter-fiber spacing. The fibers influence the average length of a solidification volume element L of the matrix and also influence the solidification time 8, of the matrix. As a result of fibers influencing L and θl, the micro-segregation in the matrix is improved when the composite contains more fibers, although the level of the improvement is slight. The Clyne-Kurz model can be used to semi-quantitatively analyze the relationship between Vf and the volume fraction .fe of the micro-segregation eutectic structure.展开更多
The effects of fiber volume fraction on damping properties of carbon fiber three-dimensional and five-directional( 3D-5Dir)braided carbon fiber / epoxyres in composite cantilever beams were studied by experimental mod...The effects of fiber volume fraction on damping properties of carbon fiber three-dimensional and five-directional( 3D-5Dir)braided carbon fiber / epoxyres in composite cantilever beams were studied by experimental modal analysis method. Meanwhile,carbon fiber plain woven laminated / epoxy resin composites with different fiber volume fraction were concerned for comparison. The experimental result of braided specimens shows that the first three orders of natural frequency increase and the first three orders of the damping ratios of specimens decrease, when the fiber volume fraction increases. Furthermore,larger fiber volume fraction will be valuable for the better anti-exiting property of braided composites,and get an opposite effect on dissipation of vibration energy. The fiber volume fraction is an important factor for vibration performance design of braided composites. The comparison between the braided specimens and laminated specimens reveals that 3D braided composites have a wider range of damping properties than laminated composites with the same fiber volume fractions.展开更多
The longitudinal tensile properties of SiCf/Ti-6Al-4V composites with different fiber volume fractions were simulated by the Monte Carlo 2-D finite element model. The random distribution of fiber strength was expresse...The longitudinal tensile properties of SiCf/Ti-6Al-4V composites with different fiber volume fractions were simulated by the Monte Carlo 2-D finite element model. The random distribution of fiber strength was expressed by the two-parameter Weibull function. Meanwhile, contact elements and birth-death elements were used to describe the interfacial sliding process after debonding and fiber breakage（or matrix cracking） respectively, which was realized by subroutine complied in ANSYS-APDL（ANSYS Parametric Design Language）. The experimental results show that the yield stress and ultimate tensile strength of SiCf/Ti-6Al-4V composites increase with increasing fiber volume fraction, while the corresponding strain of them is just on the contrary. In addition, almost the same failure mode is obtained in SiCf/Ti-6Al-4V composites with various fiber volume fractions when the interfacial shear strength is fixed. Finally, the tensile strength predicted by finite element analysis is compared with that predicted by Global load-sharing model, Local load-sharing model and conventional rule of mixtures, thus drawing the conclusion that Local load-sharing model is very perfect for the prediction of the ultimate tensile strength.展开更多
This article is concerned with the effect of rotation on the general model of the equations of the generalized thermoe- lasticity for a homogeneous isotropic elastic half-space solid, whose surface is subjected to a M...This article is concerned with the effect of rotation on the general model of the equations of the generalized thermoe- lasticity for a homogeneous isotropic elastic half-space solid, whose surface is subjected to a Mode-I crack problem. The fractional order theory of thermoelasticity is used to obtain the analytical solutions for displacement components, force stresses, and temperature. The boundary of the crack is subjected to a prescribed stress distribution and temperature. The normal mode analysis technique is used to solve the resulting non-dimensional coupled governing equations of the problem. The variations of the considered variables with the horizontal distance are illustrated graphically. Some particular cases are also discussed in the context of the problem. Effects of the fractional parameter, reinforcement, and rotation on the varia- tions of different field quantities inside the elastic medium are analyzed graphically. Comparisons are made between the results in the presence and those in the absence of fiber-reinforcing, rotating and fractional parameters.展开更多
Microstructures of laminates produced by epoxy/carbon fibers with different fiber volume fraction were studied by analyzing the composite cross-sections.The main result of the compaction of reinforcement is the flatti...Microstructures of laminates produced by epoxy/carbon fibers with different fiber volume fraction were studied by analyzing the composite cross-sections.The main result of the compaction of reinforcement is the flatting of bundle shape,the reducing of gap and the embedment of bundles among each layer.The void content outside the bundle decreased sharply during the compaction until it is less than that inside the bundle when the fiber volume fraction is over 60%.The resin flow velocity in the fiber tow is 102-104 times greater than the flow velocity out the fiber tow no matter the capillary pressure is taken into account or not.展开更多
Pulp fiber length characterization is addressed in this article. It is suggested that the proposed separation index H(L) is a viable index to the fiber fractionation performance for evaluating hydrocyclones. Fractiona...Pulp fiber length characterization is addressed in this article. It is suggested that the proposed separation index H(L) is a viable index to the fiber fractionation performance for evaluating hydrocyclones. Fractionation of softwood (coniferous wood) bleached chemithermomechanical pulp (BCTMP) fiber was carried out with a cylin- drical hydrocyclone. Pulp fiber length characteristics in different streams were examined using the fiber quality analyzer (FQA), and the cumulative fiber length fraction, the fiber length fraction density function and the separa- tion index H(L) for different streams were obtained. It is found that H(L) is very useful for characterizing the fiber fractionation performance by indicating the separation capacity of hydrocyclone for individual subgroup of fibers in different streams under different operation conditions. Results of H(L) show that there exists a critical fiber length. A higher proportion of fibers longer than the critical fiber length is in the overflow stream, and a higher proportion of fibers shorter than the critical fiber length in the underflow stream. The data obtained from FQA suggest that the split ratio is the most significant parameter for fiber fractionation performance, which is the best when the split ratio is in the range between 0.14 and 0.2. The effect of feed rate on fiber fractionation performance is weak.展开更多
This paper studied the preparation and mechanical properties of glass fiber reinforced polymer-matrix composite rings prepared by filament winding assisted by ultraviolet(UV)curing.A ray-tracing method was used to cal...This paper studied the preparation and mechanical properties of glass fiber reinforced polymer-matrix composite rings prepared by filament winding assisted by ultraviolet(UV)curing.A ray-tracing method was used to calculate the penetration ability of UV light in the resin casting,and then a typical composite ring with dual⁃curing characteristics was prepared by UV-assisted curing.The effects of winding speed and thermal initiator concentration on the distribution of fiber fraction and mechanical properties were studied.Microscopic morphology was used for the observation of the differences in fiber volume fraction.Mechanical properties tests and scanning electron micrographs were performed to investigate the failure and damage mechanisms of the composite ring samples.The ray tracing results indicate that the UV light can pass through a single yarn thickness and the energy transmitted is sufficient to cure the back side quickly.The experimental results show that the mechanical properties of the composite ring prepared in this paper are comparable to those of the heat-cured samples,which is sufficient to meet the requirements of the flywheel.展开更多
A constitutive model is constructed to consider the resin matrix post-yield softening and progressive hardening behaviors. A user-defined material mechanical behavior （UMAT） subroutine is created, then the non-linea...A constitutive model is constructed to consider the resin matrix post-yield softening and progressive hardening behaviors. A user-defined material mechanical behavior （UMAT） subroutine is created, then the non-linear three-dimensional finite element analysis on the tensile processes of multi-fiber composites is conducted. The approximate 45° shear bands emanating from the matrix crack tip are found, being coincided with the experimental observations. The shear stress on the adjacent intact fiber/matrix interface is strongly influenced by the shear band and thus the stress concentration factor （SCF） changes obviously in the adjacent fibers. The distinct stress redistribution in the adjacent intact fibers implies the significant effect of the shear bands on the progressive fiber fracture initiation. As the inter-fiber spacing increases, the peak value of the SCF in the adjacent intact fiber decreases, whereas the overload zone becomes wider. The research has provided a helpful tool to evaluate the failure of fiber composites and optimize the composite performance through the proper selection of resin matrix properties and fiber volume fraction.展开更多
This study aims for development of highly filled jute fiber reinforced composites that contains jute fiber over fiber weight fraction 60%,and jute fiber reinforced composite was fabricated by the hot-pressing method.T...This study aims for development of highly filled jute fiber reinforced composites that contains jute fiber over fiber weight fraction 60%,and jute fiber reinforced composite was fabricated by the hot-pressing method.The molding temperature was changed from 175°C to 230°C,to investigate the effect of molding temperature on the mechanical properties of jute fiber reinforced composites.The effect of surface treatment of jute fiber on the mechanical properties of jute fiber reinforced composites was also investigated.As a result,the jute fiber reinforced composites using surface treated fiber has low porosity,and the jute fiber reinforced composite having low porosity has high flexural strength and modulus.The jute fiber reinforced composite using acetone treated fiber molded at 200°C has the maximum flexural strength and modulus.展开更多
Beans are rich in dietary fiber and polyphenols;however, growing conditions may affect the occurrence of these components. The effect of irrigation and rain fed conditions on dietary fiber, indigestible fraction, poly...Beans are rich in dietary fiber and polyphenols;however, growing conditions may affect the occurrence of these components. The effect of irrigation and rain fed conditions on dietary fiber, indigestible fraction, polyphenols and antioxidant capacity of Black 8025 and Pinto Durango bean cultivars grown in Mexico have been determined. Total dietary fiber decreased in beans grown under rain fed conditions compared to those grown under irrigation. The water regimes had an effect on the total indigestible fraction for Black 8025 bean. The extractable polyphenols were affected by the water regimes, while the antioxidant capacity of extractable and non-extractable polyphenols was dependent on the bean variety. Cooking the beans altered the extractable and non-extractable polyphenols and the antioxidant capacity. Also, the antioxidant properties and some extend, the digestibility of non-digestible carbohydrates of beans were affected by water regimes. This information could be taken into account for dry bean breeding programs to improve the nutritional quality of beans.展开更多
Stochastic noises of fiber optic gyroscope （FOG） mainly contain white noise and fractal noise whose long-term dependent component causes FOG a rather slow drift. In order to eliminate this component, a two-step filt...Stochastic noises of fiber optic gyroscope （FOG） mainly contain white noise and fractal noise whose long-term dependent component causes FOG a rather slow drift. In order to eliminate this component, a two-step filtering methodology is proposed. Firstly, fractional differencing （FD） method is introduced to trans-form fractal noise into fractional white noise based on the estima-tion of Hurst exponent for long-term dependent fractal process, which together with the existing white noise make up of a gener-alized white noise. Further, an improved denoising algorithm of wavelet maxima is developed to suppress the generalized white noise. Experimental results show that the basic noise terms of FOG greatly decrease, and especially the slow drift is restrained effectively. The proposed methodology provides a promising ap-proach for filtering long-term dependent fractal noise.展开更多
The influence of volume fraction on damping capacities at room temperature for amorphous carbon fiber reinforced aluminum matrix composites was investigated.At room temperature,the dislocation damping is the primary d...The influence of volume fraction on damping capacities at room temperature for amorphous carbon fiber reinforced aluminum matrix composites was investigated.At room temperature,the dislocation damping is the primary damping mechanism.Meanwhile,the dislocation damping exhibits dynamic hysteresis at low strain amplitudes and static hysteresis at high strain amplitudes.Moreover,the damping capacity is rather sensitive to the volume fraction.Compared to unreinforced aluminum alloy,the additions of amorphous carbon fibers into the aluminum matrix can improve damping capacity below the volume fraction of 30%,whereas worsen above the volume fraction of 40%.展开更多
基金The project was financially supported by the Ministry of National Education (No.00191) and the Natural ScienceFoundation of Jiangxi Province (No.0150032)
文摘The solidification microstructures and micro-segregation of a fiber reinforced Al-9 Cu alloy, containing different volume fractions of Al2O3 short fibers about 6μm diameter and made by squeeze casting have been studied. The results indicate that as volume fraction of fiber Vf. increases, the size of final grains becomes finer in the matrix. If λf 〉λ〉1, the fibers have almost no influence on the solidification behavior of the matrix, so the final grains grow coarse, where λf is the average inter-fiber spacing and A is the secondary dendrite arm spacing. While if λf/ 〈λ〈1, the growth of crystals in the matrix is affected significantly by the fibers and the grain size is reduced to the value of the inter-fiber spacing. The fibers influence the average length of a solidification volume element L of the matrix and also influence the solidification time 8, of the matrix. As a result of fibers influencing L and θl, the micro-segregation in the matrix is improved when the composite contains more fibers, although the level of the improvement is slight. The Clyne-Kurz model can be used to semi-quantitatively analyze the relationship between Vf and the volume fraction .fe of the micro-segregation eutectic structure.
基金Tianjin Municipal Science and Technologies Commission,China(Nos.10SYSYJC27800,1ZCKFSF00500)
文摘The effects of fiber volume fraction on damping properties of carbon fiber three-dimensional and five-directional( 3D-5Dir)braided carbon fiber / epoxyres in composite cantilever beams were studied by experimental modal analysis method. Meanwhile,carbon fiber plain woven laminated / epoxy resin composites with different fiber volume fraction were concerned for comparison. The experimental result of braided specimens shows that the first three orders of natural frequency increase and the first three orders of the damping ratios of specimens decrease, when the fiber volume fraction increases. Furthermore,larger fiber volume fraction will be valuable for the better anti-exiting property of braided composites,and get an opposite effect on dissipation of vibration energy. The fiber volume fraction is an important factor for vibration performance design of braided composites. The comparison between the braided specimens and laminated specimens reveals that 3D braided composites have a wider range of damping properties than laminated composites with the same fiber volume fractions.
基金Funded by the National Natural Science Foundation of China(51271147)
文摘The longitudinal tensile properties of SiCf/Ti-6Al-4V composites with different fiber volume fractions were simulated by the Monte Carlo 2-D finite element model. The random distribution of fiber strength was expressed by the two-parameter Weibull function. Meanwhile, contact elements and birth-death elements were used to describe the interfacial sliding process after debonding and fiber breakage（or matrix cracking） respectively, which was realized by subroutine complied in ANSYS-APDL（ANSYS Parametric Design Language）. The experimental results show that the yield stress and ultimate tensile strength of SiCf/Ti-6Al-4V composites increase with increasing fiber volume fraction, while the corresponding strain of them is just on the contrary. In addition, almost the same failure mode is obtained in SiCf/Ti-6Al-4V composites with various fiber volume fractions when the interfacial shear strength is fixed. Finally, the tensile strength predicted by finite element analysis is compared with that predicted by Global load-sharing model, Local load-sharing model and conventional rule of mixtures, thus drawing the conclusion that Local load-sharing model is very perfect for the prediction of the ultimate tensile strength.
文摘This article is concerned with the effect of rotation on the general model of the equations of the generalized thermoe- lasticity for a homogeneous isotropic elastic half-space solid, whose surface is subjected to a Mode-I crack problem. The fractional order theory of thermoelasticity is used to obtain the analytical solutions for displacement components, force stresses, and temperature. The boundary of the crack is subjected to a prescribed stress distribution and temperature. The normal mode analysis technique is used to solve the resulting non-dimensional coupled governing equations of the problem. The variations of the considered variables with the horizontal distance are illustrated graphically. Some particular cases are also discussed in the context of the problem. Effects of the fractional parameter, reinforcement, and rotation on the varia- tions of different field quantities inside the elastic medium are analyzed graphically. Comparisons are made between the results in the presence and those in the absence of fiber-reinforcing, rotating and fractional parameters.
基金The Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry,Science and Technology Commission of Shanghai Municipality,China(No.06QA14001)
文摘Microstructures of laminates produced by epoxy/carbon fibers with different fiber volume fraction were studied by analyzing the composite cross-sections.The main result of the compaction of reinforcement is the flatting of bundle shape,the reducing of gap and the embedment of bundles among each layer.The void content outside the bundle decreased sharply during the compaction until it is less than that inside the bundle when the fiber volume fraction is over 60%.The resin flow velocity in the fiber tow is 102-104 times greater than the flow velocity out the fiber tow no matter the capillary pressure is taken into account or not.
基金Supported by the Natural Science and Engineering Research Council of Canada.
文摘Pulp fiber length characterization is addressed in this article. It is suggested that the proposed separation index H(L) is a viable index to the fiber fractionation performance for evaluating hydrocyclones. Fractionation of softwood (coniferous wood) bleached chemithermomechanical pulp (BCTMP) fiber was carried out with a cylin- drical hydrocyclone. Pulp fiber length characteristics in different streams were examined using the fiber quality analyzer (FQA), and the cumulative fiber length fraction, the fiber length fraction density function and the separa- tion index H(L) for different streams were obtained. It is found that H(L) is very useful for characterizing the fiber fractionation performance by indicating the separation capacity of hydrocyclone for individual subgroup of fibers in different streams under different operation conditions. Results of H(L) show that there exists a critical fiber length. A higher proportion of fibers longer than the critical fiber length is in the overflow stream, and a higher proportion of fibers shorter than the critical fiber length in the underflow stream. The data obtained from FQA suggest that the split ratio is the most significant parameter for fiber fractionation performance, which is the best when the split ratio is in the range between 0.14 and 0.2. The effect of feed rate on fiber fractionation performance is weak.
基金supported by the National Key Laboratory of Science and Technology on Helicopter Transmission(Nanjing University of Aeronautics and Astronautics)(No.HTL-A-20K01)the Pretension and Relaxation Mechanism of Thermoplastic Prepreg Tape Winding with Tension Used to Hi-Speed Permanent Magnet Machine Sleeve(No.51903249)the Priority Academic Program Development of Jiangsu Higher Education Institutions and the Fundamental Research Funds for the Central Universities。
文摘This paper studied the preparation and mechanical properties of glass fiber reinforced polymer-matrix composite rings prepared by filament winding assisted by ultraviolet(UV)curing.A ray-tracing method was used to calculate the penetration ability of UV light in the resin casting,and then a typical composite ring with dual⁃curing characteristics was prepared by UV-assisted curing.The effects of winding speed and thermal initiator concentration on the distribution of fiber fraction and mechanical properties were studied.Microscopic morphology was used for the observation of the differences in fiber volume fraction.Mechanical properties tests and scanning electron micrographs were performed to investigate the failure and damage mechanisms of the composite ring samples.The ray tracing results indicate that the UV light can pass through a single yarn thickness and the energy transmitted is sufficient to cure the back side quickly.The experimental results show that the mechanical properties of the composite ring prepared in this paper are comparable to those of the heat-cured samples,which is sufficient to meet the requirements of the flywheel.
基金financially supported by the National Key Basic Research Program of China(No.2010CB631102)the National Natural Science Foundation of China(Nos.51173100 and 51373090)the Natural Science Foundation of Shandong Province(No.JQ201016)
文摘A constitutive model is constructed to consider the resin matrix post-yield softening and progressive hardening behaviors. A user-defined material mechanical behavior （UMAT） subroutine is created, then the non-linear three-dimensional finite element analysis on the tensile processes of multi-fiber composites is conducted. The approximate 45° shear bands emanating from the matrix crack tip are found, being coincided with the experimental observations. The shear stress on the adjacent intact fiber/matrix interface is strongly influenced by the shear band and thus the stress concentration factor （SCF） changes obviously in the adjacent fibers. The distinct stress redistribution in the adjacent intact fibers implies the significant effect of the shear bands on the progressive fiber fracture initiation. As the inter-fiber spacing increases, the peak value of the SCF in the adjacent intact fiber decreases, whereas the overload zone becomes wider. The research has provided a helpful tool to evaluate the failure of fiber composites and optimize the composite performance through the proper selection of resin matrix properties and fiber volume fraction.
文摘This study aims for development of highly filled jute fiber reinforced composites that contains jute fiber over fiber weight fraction 60%,and jute fiber reinforced composite was fabricated by the hot-pressing method.The molding temperature was changed from 175°C to 230°C,to investigate the effect of molding temperature on the mechanical properties of jute fiber reinforced composites.The effect of surface treatment of jute fiber on the mechanical properties of jute fiber reinforced composites was also investigated.As a result,the jute fiber reinforced composites using surface treated fiber has low porosity,and the jute fiber reinforced composite having low porosity has high flexural strength and modulus.The jute fiber reinforced composite using acetone treated fiber molded at 200°C has the maximum flexural strength and modulus.
文摘Beans are rich in dietary fiber and polyphenols;however, growing conditions may affect the occurrence of these components. The effect of irrigation and rain fed conditions on dietary fiber, indigestible fraction, polyphenols and antioxidant capacity of Black 8025 and Pinto Durango bean cultivars grown in Mexico have been determined. Total dietary fiber decreased in beans grown under rain fed conditions compared to those grown under irrigation. The water regimes had an effect on the total indigestible fraction for Black 8025 bean. The extractable polyphenols were affected by the water regimes, while the antioxidant capacity of extractable and non-extractable polyphenols was dependent on the bean variety. Cooking the beans altered the extractable and non-extractable polyphenols and the antioxidant capacity. Also, the antioxidant properties and some extend, the digestibility of non-digestible carbohydrates of beans were affected by water regimes. This information could be taken into account for dry bean breeding programs to improve the nutritional quality of beans.
基金supported by Aviation Science Foundation(20070851011).
文摘Stochastic noises of fiber optic gyroscope （FOG） mainly contain white noise and fractal noise whose long-term dependent component causes FOG a rather slow drift. In order to eliminate this component, a two-step filtering methodology is proposed. Firstly, fractional differencing （FD） method is introduced to trans-form fractal noise into fractional white noise based on the estima-tion of Hurst exponent for long-term dependent fractal process, which together with the existing white noise make up of a gener-alized white noise. Further, an improved denoising algorithm of wavelet maxima is developed to suppress the generalized white noise. Experimental results show that the basic noise terms of FOG greatly decrease, and especially the slow drift is restrained effectively. The proposed methodology provides a promising ap-proach for filtering long-term dependent fractal noise.
文摘The influence of volume fraction on damping capacities at room temperature for amorphous carbon fiber reinforced aluminum matrix composites was investigated.At room temperature,the dislocation damping is the primary damping mechanism.Meanwhile,the dislocation damping exhibits dynamic hysteresis at low strain amplitudes and static hysteresis at high strain amplitudes.Moreover,the damping capacity is rather sensitive to the volume fraction.Compared to unreinforced aluminum alloy,the additions of amorphous carbon fibers into the aluminum matrix can improve damping capacity below the volume fraction of 30%,whereas worsen above the volume fraction of 40%.
