The surface treatment of silca fume with silane coupling agent prior w incorporation in a cement mortar resulted in composites exhibiting increuses in loss tangent by 5%-200% and storage modulus by 10%-20% , relative...The surface treatment of silca fume with silane coupling agent prior w incorporation in a cement mortar resulted in composites exhibiting increuses in loss tangent by 5%-200% and storage modulus by 10%-20% , relative to the value obtained by using as-received silica fume. The scanning electron microscopy （SEM） images iindicate that there is a morphological difference in the cement paste with treated and as-received silica fume, The, X-ray diffraction （XRD）, infrared （IR） spectrum analyses and mercury intrusion porosimetry （ MIP ） have provided evidence to understand the reaction mechanism between treated silica .fume and the hydrate product of cement. This has led to the establishment of an initial microscopic model describing the damping behavior of cement matrix.展开更多
Based on the linear theories of thin cylindrical shells and viscoelastic materials, a governing equation describing vibration of a sandwich circular cylindrical shell with a viscoelastic core under harmonic excitation...Based on the linear theories of thin cylindrical shells and viscoelastic materials, a governing equation describing vibration of a sandwich circular cylindrical shell with a viscoelastic core under harmonic excitation is derived. The equation can be written as a matrix differential equation of the first order, and is obtained by considering the energy dissipation due to the shear deformation of the viscoelastic core layer and the interaction between all layers. A new matrix method for solving the governing equation is then presented With an extended homogeneous capacity precision integration approach. Having obtained these, vibration characteristics and damping effect of the sandwich cylindrical shell can be studied. The method differs from a recently published work as the state vector in the governing equation is composed of displacements and internal forces of the sandwich shell rather than displacements and their derivatives. So the present method can be applied to solve dynamic problems of the kind of sandwich shells with various boundary conditions and partially constrained layer damping. Numerical examples show that the proposed approach is effective and reliable compared with the existing methods.展开更多
Magnesium alloy reinforced with 8% TiC(mass fraction) is in-situ synthesized using remelting and dilution technique. Damping capacity of AZ91 alloy and magnesium matrix composites was examined using Mark IV dynamic me...Magnesium alloy reinforced with 8% TiC(mass fraction) is in-situ synthesized using remelting and dilution technique. Damping capacity of AZ91 alloy and magnesium matrix composites was examined using Mark IV dynamic mechanical thermal analyzer. The results reveal that the damping capacity of materials is independent of frequency, but dependent on strain. Damping capacity of materials increase when testing strain enhances, and there is strain peak at damping-strain curve of materials. There are two temperature peaks at damping-temperature curve of magnesium matrix composites under 140℃ and 250℃ respectively. The damping mechanism is explained by dislocation motion, interface slip and grain boundary slip.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
The hollow sphere fly ash/6061Al composite with about 43% porosity in volume fraction (produced by the addition of hollow sphere fly ash particles) was fabricated by squeeze casting technique. Using the same technique...The hollow sphere fly ash/6061Al composite with about 43% porosity in volume fraction (produced by the addition of hollow sphere fly ash particles) was fabricated by squeeze casting technique. Using the same technique, the fly ash/7075Al composite with all the porosity in hollow sphere fly ash infiltrated by molten aluminum was fabricated for partially studying the effect of porosity on the damping behavior of the fly ash/Al composites. The resonant damping capacity of the 'porous' fly ash/6061Al composite reached (20.2-26.9)×10-3 and was about 8 times of the value tested by forced vibration method (in the frequency range 0.2-2 Hz). However, the damping capacity of the as-received 6061Al and the 'dense' fly ash/7075Al composite were consistent by the two testing methods and were in the range of (1.1-7.7)×10-3. The effect of temperature on the damping behavior of the materials was also studied. The related damping mechanisms have also been discussed in light of data from the characterization of microstructure and damping capacity. Due to the inferior mechanical properties of the fly ash particles, the tensile strength of the FA/Al composites was lower than that of the corresponding aluminum alloy matrix and was 70.1 MPa and 180.6 MPa for the 'porous' fly ash/6061Al and 'dense' fly ash/7075Al composite, respectively.展开更多
A new matrix perturbation analysis method is presented for efficient approximate solution of the complex modal quadratic generalized eigenvalue problem of viscously damped linear vibration systems. First, the damping ...A new matrix perturbation analysis method is presented for efficient approximate solution of the complex modal quadratic generalized eigenvalue problem of viscously damped linear vibration systems. First, the damping matrix is decomposed into the sum of a proportional-and a nonproportional-damping parts, and the solutions of the real modal eigenproblem with the proportional dampings are determined, which are a set of initial approximate solutions of the complex modal eigenproblem. Second, by taking the nonproportional-damping part as a small modification to the proportional one and using the matrix perturbation analysis method, a set of approximate solutions of the complex modal eigenvalue problem can be obtained analytically. The result is quite simple. The new method is applicable to the systems with viscous dampings-which do not deviate far away from the proportional-damping case. It is particularly important that the solution technique be also effective to the systems with heavy, but not over, dampings. The solution formulas of complex modal eigenvlaues and eigenvectors are derived up to second-order perturbation terms. The effectiveness of the perturbation algorithm is illustrated by an exemplar numerical problem with heavy dampings. In addition, the practicability of approximately estimating the complex modal eigenvalues, under the proportional-damping hypothesis, of damped vibration systems is discussed by several numerical examples.展开更多
SiCp/Gr/2024Al metal matrix composites were processed by squeeze casting technology. The microstructure of composites was observed by SEM and TEM, and the effects of graphite particulates and SiC particulates on the d...SiCp/Gr/2024Al metal matrix composites were processed by squeeze casting technology. The microstructure of composites was observed by SEM and TEM, and the effects of graphite particulates and SiC particulates on the damping behaviors of composites were also investigated. The results show that the microstructure of composites was dense and homogeneous, without any interfacial reactivity among reinforcement/matrix interfaces. Compared with the damping capacity of 2024A1, the damping capacity of composites was enhanced significantly by addition of SiC or graphite particulates. The main damping mechanisms of SiCp/Al composites were ascribed to the dislocation damping, and those of SiCp/Gr/2024Al were attributed to the intrinsic damping and interface damping.展开更多
Two very important factors which determine the effectiveness of a pump are its volumetric and power efficiencies. Yin and Ghoneim constructed a prototype of a Flexible-Matrix-Composite (FMC) body pump with a very high...Two very important factors which determine the effectiveness of a pump are its volumetric and power efficiencies. Yin and Ghoneim constructed a prototype of a Flexible-Matrix-Composite (FMC) body pump with a very high volumetric efficiency or pumping potential (the relative volume reduction due to a relative input stroke). The high volumetric efficiency is attributed to the geometry of the pump’s structure (hyperboloid) as well as the high negative effective Poisson’s ratio of the 3-layer [θ/β/θ] flexible-matrix-composite (carbon/polyurethane) laminate adopted for the body of the pump. However, the power efficiency of the pump was not evaluated. It is the objective of the current paper to obtain an estimate of the power efficiency of the pump. The viscoelastic properties of the 3-layer FMC (carbon/polyurethane) laminate are evaluated experimentally using the Dynamic Mechanical Analyzer (DMA) as well as analytically by applying the correspondence principle together with the micro-mechanics approach. In order to obtain an estimate of the power efficiency of the FMC body pump, the axial and shear loss factors of a laminated infinitely long cylindrical tube as functions of β and θ fiber orientation angles are determined employing the Adam and Bacon approach. The analysis engenders high loss factors (greater than 0.4), which suggests that the power efficiency of the proposed pump using the 3-layer carbon/polyurethane laminate may be low.展开更多
目的探讨三乌胶丸治疗寒湿痹阻证膝骨关节炎的疗效。方法按照随机数表法将304例膝骨关节炎患者分为对照组和研究组,各152例。对照组给予美洛昔康片、硫酸氨基葡萄糖片治疗,研究组在对照组基础上加用三乌胶丸治疗,均治疗28 d。比较2组治...目的探讨三乌胶丸治疗寒湿痹阻证膝骨关节炎的疗效。方法按照随机数表法将304例膝骨关节炎患者分为对照组和研究组,各152例。对照组给予美洛昔康片、硫酸氨基葡萄糖片治疗,研究组在对照组基础上加用三乌胶丸治疗,均治疗28 d。比较2组治疗28 d后的疗效,治疗前和治疗28 d后的中医症状、膝关节功能、疼痛情况、骨代谢指标、血清基质金属蛋白酶-1(matrix metalloproteinase-1,MMP-1)、基质金属蛋白酶-3(MMP-3)、Smad-1水平及治疗期间的安全性。结果研究组治疗28 d后的总有效率(93.42%,142/152)高于对照组(78.95%,120/152)(P<0.05)。治疗28 d后,2组中医症状、西安大略麦克马斯特大学骨关节炎指数(Western Ontario and McMaster University Osteoarthritis Index,WOAMC)、视觉模拟评分法(visual analog scale,VAS)评分及血清MMP-1、MMP-3水平与治疗前比较降低,研究组低于对照组(P<0.05);血清骨特异性碱性磷酸酶(bone-specifi c alkaline phosphatase,BALP)、骨保护素(osteoprotegerin,OPG)、骨钙素(bone gla-protein,BGP)、Smad-1水平升高,研究组高于对照组(P<0.05)。研究组治疗期间不良反应总发生率低于对照组(P<0.05)。结论三乌胶丸可调节寒湿痹阻证膝骨关节炎患者血清MMP-1、MMP-3、Smad-1及骨代谢指标水平,促进软骨修复,改善患者中医症状、膝关节功能,减轻疼痛程度,提高疗效和安全性。展开更多
In this study, through novel drift-based equations of motion in the frequency domain, optimum placement and characteristics of linear velocity-dependent dampers are investigated. In this study, the sum of the square o...In this study, through novel drift-based equations of motion in the frequency domain, optimum placement and characteristics of linear velocity-dependent dampers are investigated. In this study, the sum of the square of the absolute values of transfer matrix elements for interstory drifts is considered as the optimization index. Optimum placement and characteristics of dampers are simultaneously obtained by minimizing the optimization index through an incremental procedure. In each step of the procedure, a predefined value is considered as the damper characteristic. The optimum story for this increment is selected such that it leads to a minimum value for the optimization index. The procedure is repeated for the next increments until the optimization index meets its target value, which is obtained according to the desired damping ratio for the overall structure. In other words, the desired overall damping ratio is the input to the proposed procedure, and the optimal placement and characteristics of the dampers are its output. It is observed that the optimal placement of a velocitydependent damper depends on the damping coefficient of the added damper, frequency of the excitation, and distribution of the mass, stiffness, and inherent damping of the main structure.展开更多
文摘The surface treatment of silca fume with silane coupling agent prior w incorporation in a cement mortar resulted in composites exhibiting increuses in loss tangent by 5%-200% and storage modulus by 10%-20% , relative to the value obtained by using as-received silica fume. The scanning electron microscopy （SEM） images iindicate that there is a morphological difference in the cement paste with treated and as-received silica fume, The, X-ray diffraction （XRD）, infrared （IR） spectrum analyses and mercury intrusion porosimetry （ MIP ） have provided evidence to understand the reaction mechanism between treated silica .fume and the hydrate product of cement. This has led to the establishment of an initial microscopic model describing the damping behavior of cement matrix.
基金supported by the National Natural Science Foundation of China (No. 10662003)the Doctoral Fund of Ministry of Education of China (No. 20040787013)
文摘Based on the linear theories of thin cylindrical shells and viscoelastic materials, a governing equation describing vibration of a sandwich circular cylindrical shell with a viscoelastic core under harmonic excitation is derived. The equation can be written as a matrix differential equation of the first order, and is obtained by considering the energy dissipation due to the shear deformation of the viscoelastic core layer and the interaction between all layers. A new matrix method for solving the governing equation is then presented With an extended homogeneous capacity precision integration approach. Having obtained these, vibration characteristics and damping effect of the sandwich cylindrical shell can be studied. The method differs from a recently published work as the state vector in the governing equation is composed of displacements and internal forces of the sandwich shell rather than displacements and their derivatives. So the present method can be applied to solve dynamic problems of the kind of sandwich shells with various boundary conditions and partially constrained layer damping. Numerical examples show that the proposed approach is effective and reliable compared with the existing methods.
文摘Magnesium alloy reinforced with 8% TiC(mass fraction) is in-situ synthesized using remelting and dilution technique. Damping capacity of AZ91 alloy and magnesium matrix composites was examined using Mark IV dynamic mechanical thermal analyzer. The results reveal that the damping capacity of materials is independent of frequency, but dependent on strain. Damping capacity of materials increase when testing strain enhances, and there is strain peak at damping-strain curve of materials. There are two temperature peaks at damping-temperature curve of magnesium matrix composites under 140℃ and 250℃ respectively. The damping mechanism is explained by dislocation motion, interface slip and grain boundary slip.
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%.
文摘The hollow sphere fly ash/6061Al composite with about 43% porosity in volume fraction (produced by the addition of hollow sphere fly ash particles) was fabricated by squeeze casting technique. Using the same technique, the fly ash/7075Al composite with all the porosity in hollow sphere fly ash infiltrated by molten aluminum was fabricated for partially studying the effect of porosity on the damping behavior of the fly ash/Al composites. The resonant damping capacity of the 'porous' fly ash/6061Al composite reached (20.2-26.9)×10-3 and was about 8 times of the value tested by forced vibration method (in the frequency range 0.2-2 Hz). However, the damping capacity of the as-received 6061Al and the 'dense' fly ash/7075Al composite were consistent by the two testing methods and were in the range of (1.1-7.7)×10-3. The effect of temperature on the damping behavior of the materials was also studied. The related damping mechanisms have also been discussed in light of data from the characterization of microstructure and damping capacity. Due to the inferior mechanical properties of the fly ash particles, the tensile strength of the FA/Al composites was lower than that of the corresponding aluminum alloy matrix and was 70.1 MPa and 180.6 MPa for the 'porous' fly ash/6061Al and 'dense' fly ash/7075Al composite, respectively.
文摘A new matrix perturbation analysis method is presented for efficient approximate solution of the complex modal quadratic generalized eigenvalue problem of viscously damped linear vibration systems. First, the damping matrix is decomposed into the sum of a proportional-and a nonproportional-damping parts, and the solutions of the real modal eigenproblem with the proportional dampings are determined, which are a set of initial approximate solutions of the complex modal eigenproblem. Second, by taking the nonproportional-damping part as a small modification to the proportional one and using the matrix perturbation analysis method, a set of approximate solutions of the complex modal eigenvalue problem can be obtained analytically. The result is quite simple. The new method is applicable to the systems with viscous dampings-which do not deviate far away from the proportional-damping case. It is particularly important that the solution technique be also effective to the systems with heavy, but not over, dampings. The solution formulas of complex modal eigenvlaues and eigenvectors are derived up to second-order perturbation terms. The effectiveness of the perturbation algorithm is illustrated by an exemplar numerical problem with heavy dampings. In addition, the practicability of approximately estimating the complex modal eigenvalues, under the proportional-damping hypothesis, of damped vibration systems is discussed by several numerical examples.
文摘SiCp/Gr/2024Al metal matrix composites were processed by squeeze casting technology. The microstructure of composites was observed by SEM and TEM, and the effects of graphite particulates and SiC particulates on the damping behaviors of composites were also investigated. The results show that the microstructure of composites was dense and homogeneous, without any interfacial reactivity among reinforcement/matrix interfaces. Compared with the damping capacity of 2024A1, the damping capacity of composites was enhanced significantly by addition of SiC or graphite particulates. The main damping mechanisms of SiCp/Al composites were ascribed to the dislocation damping, and those of SiCp/Gr/2024Al were attributed to the intrinsic damping and interface damping.
文摘Two very important factors which determine the effectiveness of a pump are its volumetric and power efficiencies. Yin and Ghoneim constructed a prototype of a Flexible-Matrix-Composite (FMC) body pump with a very high volumetric efficiency or pumping potential (the relative volume reduction due to a relative input stroke). The high volumetric efficiency is attributed to the geometry of the pump’s structure (hyperboloid) as well as the high negative effective Poisson’s ratio of the 3-layer [θ/β/θ] flexible-matrix-composite (carbon/polyurethane) laminate adopted for the body of the pump. However, the power efficiency of the pump was not evaluated. It is the objective of the current paper to obtain an estimate of the power efficiency of the pump. The viscoelastic properties of the 3-layer FMC (carbon/polyurethane) laminate are evaluated experimentally using the Dynamic Mechanical Analyzer (DMA) as well as analytically by applying the correspondence principle together with the micro-mechanics approach. In order to obtain an estimate of the power efficiency of the FMC body pump, the axial and shear loss factors of a laminated infinitely long cylindrical tube as functions of β and θ fiber orientation angles are determined employing the Adam and Bacon approach. The analysis engenders high loss factors (greater than 0.4), which suggests that the power efficiency of the proposed pump using the 3-layer carbon/polyurethane laminate may be low.
文摘目的探讨三乌胶丸治疗寒湿痹阻证膝骨关节炎的疗效。方法按照随机数表法将304例膝骨关节炎患者分为对照组和研究组,各152例。对照组给予美洛昔康片、硫酸氨基葡萄糖片治疗,研究组在对照组基础上加用三乌胶丸治疗,均治疗28 d。比较2组治疗28 d后的疗效,治疗前和治疗28 d后的中医症状、膝关节功能、疼痛情况、骨代谢指标、血清基质金属蛋白酶-1(matrix metalloproteinase-1,MMP-1)、基质金属蛋白酶-3(MMP-3)、Smad-1水平及治疗期间的安全性。结果研究组治疗28 d后的总有效率(93.42%,142/152)高于对照组(78.95%,120/152)(P<0.05)。治疗28 d后,2组中医症状、西安大略麦克马斯特大学骨关节炎指数(Western Ontario and McMaster University Osteoarthritis Index,WOAMC)、视觉模拟评分法(visual analog scale,VAS)评分及血清MMP-1、MMP-3水平与治疗前比较降低,研究组低于对照组(P<0.05);血清骨特异性碱性磷酸酶(bone-specifi c alkaline phosphatase,BALP)、骨保护素(osteoprotegerin,OPG)、骨钙素(bone gla-protein,BGP)、Smad-1水平升高,研究组高于对照组(P<0.05)。研究组治疗期间不良反应总发生率低于对照组(P<0.05)。结论三乌胶丸可调节寒湿痹阻证膝骨关节炎患者血清MMP-1、MMP-3、Smad-1及骨代谢指标水平,促进软骨修复,改善患者中医症状、膝关节功能,减轻疼痛程度,提高疗效和安全性。
基金National Natural Science Foundation of China Under Grant No.50638010the Foundation of Ministry of Education for Innovation Group Under Grant No.IRT0518
文摘In this study, through novel drift-based equations of motion in the frequency domain, optimum placement and characteristics of linear velocity-dependent dampers are investigated. In this study, the sum of the square of the absolute values of transfer matrix elements for interstory drifts is considered as the optimization index. Optimum placement and characteristics of dampers are simultaneously obtained by minimizing the optimization index through an incremental procedure. In each step of the procedure, a predefined value is considered as the damper characteristic. The optimum story for this increment is selected such that it leads to a minimum value for the optimization index. The procedure is repeated for the next increments until the optimization index meets its target value, which is obtained according to the desired damping ratio for the overall structure. In other words, the desired overall damping ratio is the input to the proposed procedure, and the optimal placement and characteristics of the dampers are its output. It is observed that the optimal placement of a velocitydependent damper depends on the damping coefficient of the added damper, frequency of the excitation, and distribution of the mass, stiffness, and inherent damping of the main structure.
