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1.
电流变液在两平行电极板间流动行为的实验研究   总被引:2,自引:0,他引:2  
通过实验的方法研究了电流变液流经两间距为1.1mm的平行电极板的流动行为,实验所观测到的由于电流变液在电场作用下非均匀固化所引起的固相颗粒淤积与饱和过程、河道分岔和失稳等现象,对现有的有关电流变阀均匀流动模型提出了质疑,这为进一步深入理解电流变液的力学行为,建立新的理论模型提供了实验依据  相似文献   

2.
电流变阻尼器动力特性的研究   总被引:6,自引:0,他引:6  
电流变液是一种可控流体,它在电场的作用下可从牛顿流体变为屈服剪应力较高的粘塑性体,且这种变化连续,可逆,迅速。本文在简要介绍了电流变阻尼器的原理和特点后,就电流变阻尼器的动力特性,如流量和阻尼力等,建立模型,将流体流动分为剪切流动和压差流动两种情况进行了讨论,并进行迭加,使流量和阻尼计算公式得到修正和完善,最后对阻尼力进行简化,提出压差流动占绝对优势,完全可以反映电流变阻尼器的阻尼特性,为进一步实现对阻尼器的控制提供了理论基础。  相似文献   

3.
汶川大地震后水坝建设中若干问题的思考   总被引:1,自引:0,他引:1  
陈德基 《力学学报》2009,17(3):289-295
应用参数摄动法对可压缩N-S方程进行渐近展开,并取其零阶近似对高压下微管道液体流动 特性进行了分析.对任意截面形状和面积的微管道,在等温流动假设下将其截面形状、滑移 长度等对解的贡献转化为求解该截面的格林函数,并给出等截面圆形微管道流动的零阶近似 解.以此分析可压缩性、黏性以及壁面滑移等因素对高压下液体微管道流动特性的影响,进 一步揭示了高压驱动下液体微管道流动偏离经典Hagen-Poiseuille(HP)理论的原因.  相似文献   

4.
非线性压电效应下压电弯曲执行器的动力分析   总被引:4,自引:1,他引:3  
姚林泉  丁睿 《力学学报》2005,37(2):183-189
研究压电弯曲执行器在强电场作用下的非线性动力行为.考虑电致伸缩和电致弹性的非线性压电效应,导出了压电悬臂执行器变刚度的弯曲振动控制方程.利用非定常振动的渐近理论,讨论了弯曲压电执行器的动力特征.根据目前的非线性模型可以计算压电悬臂执行器的固有共振频率与电场的变化关系.结果表明压电执行器端头挠度谐振幅度随作用电场振幅的增大而增大,以及力学品质因数随电场振幅的增大而减少,并且与实验结果非常吻合.通过数值比较得到在电场频率随时间变化非常缓慢的情况下非定常振动问题可以近似地用定常振动来处理.  相似文献   

5.
电流变悬浮液内部结构对外电场的快速响应发生在指定的控制空间中,在这一特指的时间和空间尺度上电流变悬浮液的物理行为特征主要为剪切速率低和流动阻尼大,即Mach和Reynolds数一般不大,可以视为微尺度流动来加以研究。针对这一流动特征,基于介观动理论的格子Boltzmann方法,建立了电流变悬浮液两相流动的离散颗粒运动模型,通过该模型进行了动力学模拟,结果表明,该模型解决了分子动力学模型难以描述的因颗粒运动造成局部流场流变特性改变的难题,以及该流场双向耦合过程中对颗粒运动的影响。  相似文献   

6.
电流变液和电流变效应   总被引:26,自引:1,他引:25  
朱克勤  陶荣甲 《力学进展》1994,24(2):154-162
电流变液是一种极有发展前景的新颖材料,通常由不导电的母液和均匀散布在其中的电介质微粒组成。对于外加电场的变化,它的力学性能可以作出迅速的响应,因而在工业上极具应用前景。本文将就电流变液的研究进行综述,涉及的内容有:电流变效应的机理、电流变液材料及其力学性能、应用和展望.  相似文献   

7.
应用参数摄动法对可压缩N-S方程进行渐近展开,并取其零阶近似对高压下微管道液体流动特性进行了分析.对任意截面形状和面积的微管道,在等温流动假设下将其截面形状、滑移长度等对解的贡献转化为求解该截面的格林函数,并给出等截面圆形微管道流动的零阶近似解.以此分析可压缩性、黏性以及壁面滑移等因素对高压下液体微管道流动特性的影响,进一步揭示了高压驱动下液体微管道流动偏离经典 Hagen-Poiseuille(HP)理论的原因.  相似文献   

8.
用 HAAKE RV2 0型流变仪 ,在不同外加电场强度和不同颗粒体积分数下测试了基于沸石和硅油的电流变液的剪切应力变化 .结果表明 :随着外加电场强度升高 ,电流变液的零电场粘度急剧增加 ,电流变液的剪切屈服应力增加 ;随着电流变液中沸石颗粒体积分数升高 ,电流变液的剪切屈服强度急剧上升 .这种变化可以用颗粒间作用力与颗粒间距的关系、单位面积的颗粒链数目变化以及多体作用对电流变液性能的影响来解释  相似文献   

9.
针对超导-永磁悬浮系统,分别采用描述超导宏观电磁场本构关系的磁通流动模型和磁通流动与蠕动模型,定量模拟了自由悬浮于超导体上方永磁体的振动。通过比较研究说明磁通蠕动效应对超导悬浮动力运动的影响程度以及这一影响随超导临界电流密度、系统外加激励振幅和频率的变化规律。  相似文献   

10.
本文介绍了如何用云纹干涉法实时地观察铁电陶瓷在力载荷和电载荷共同作用下裂尖的破坏行为.测量了三点弯试验中由电场和应力集中导致的裂尖的变形场.对变形的云纹图分析表明:当极化方向与裂纹扩展方向一致,且都与电场方向垂直,裂尖附近的正应变随电场的增加而增加,应变集中现象比较突出,电场促进和加速了裂纹的扩展.  相似文献   

11.
The change in the viscosity of deionized aqueous hectorite suspensions by applying an electric field was investigated. The deionized suspensions had low viscosity, which was almost the same as that of its solvent, water. Upon applying a DC electric field of the order of a few volt per millimeter to the deionized suspension, the viscosity started to increase gradually and reached a constant value that was high enough relative to the original value. Regarding the mechanism of the electrically induced stress increase, it is highly plausible that a three-dimensional network structure formed under the electric field due to a deformation of the electrical double layer.  相似文献   

12.
The rheological characterizations of concentrated suspensions are generally carried out assuming “well-mixed” suspensions. However, the variation of the concentration distributions of the ingredients of the formulation, i.e., the “goodness of mixing”, the size and shape distributions of the particle clusters and the rheological behavior of the suspension all depend on the thermo-mechanical history that the suspension is exposed to during the mixing process. Here, various experimental tools are used for the characterization of the degree of mixedness (concentration distributions) of various ingredients along with the characterization of rheological material functions, wall slip behavior and the maximum packing fraction of a graphite/elastomer suspension. The degree of mixedness values of the ingredients of the suspensions processed using batch and continuous processes and under differing operating conditions were characterized quantitatively using wide-angle X-ray diffraction and thermo gravimetric analysis and were elucidated under the light of the electrical properties of the suspension as affected by the mixing process. Upon achieving better homogeneity of the graphite particles and the binder and decreases in the size and breadth of the size distributions of particle clusters (as inferred from electrical measurements and maximum packing fraction values), the elasticity (storage modulus) and the shear viscosity (magnitude of the complex viscosity from small-amplitude oscillatory shear and shear viscosity from steady torsional and capillary rheometry) of the suspension decreased significantly and the wall slip velocity values increased. These findings demonstrate the intimate relationships that exist between the rheological behavior of concentrated suspensions and the thermo-mechanical history that they are exposed to during the processing stage and suggest that the preparation conditions for suspensions should be carefully selected and well documented to achieve reproducible characterization of rheological material functions.  相似文献   

13.
We study on a suspension of poly(N-isopropylacrylamide) at a low concentration using particle-tracking microrheology in two modalities: at constant temperatures and during a heating ramp. The dilute suspensions do not present a glass state at low temperatures, and at high temperatures, the polymer particles collapse, giving rise to entropic forces that induce aggregation of the tracking colloids. The viscoelastic moduli of the system, which drastically change with temperature, allow us to follow this dynamics. Furthermore, the viscosity of the system remains approximately constant with temperature but suddenly increases as it passes the lower critical solution temperature (LCST). Such effect is probably associated to hydration before the collapse of the polymer, as verified by electrical conductivity measurements.  相似文献   

14.
Multimodal suspensions, consisting of non-colloidal spherical particles and a Newtonian matrix, are considered. A new differential (or multi-scale mean field approach) model for the relative viscosity of multimodal suspensions has been developed. The problem of the random close packing fraction of the solid phase is also investigated. We suppose that the multimodal suspension has a dominant large particle composition and that the smaller particles are embedded in the empty space between the larger particles. The relative viscosity model can therefore be based on the theory of monomodal suspensions. Experimental data of Eveson are compared to the predictions given by using three different models of monomodal suspensions respectively. The Maron–Pierce approach appears to give the best agreement with Eveson’s experiments. However, due to experimental uncertainties, we recommend that the Mendoza and Santamaria-Holek (MSH) formula be adopted.  相似文献   

15.
通过实验方法研究了加入TiO2纳米颗粒的相变悬浮液流变特性. 研究表明,加入纳米颗 粒的相变悬浮液仍可被视为牛顿流体,温度对悬浮液的黏性系数有显著影响,其黏性系数随 温度变化的趋势与基液一致. 悬浮液的黏性随纳米颗粒浓度增加以非线性方式增加,当纳米 颗粒的质量浓度为5{\%}时,黏性的增量大约为23%.  相似文献   

16.
The steady-shear viscosity, dynamic viscoelasticity, and sedimentation behavior were measured for silica suspensions dispersed in aqueous solutions of poly(ethylene oxide) (PEO). For suspensions prepared with polymer solutions in which the transient network is developed by entanglements, the viscosity at a given shear rate decreases, shows a minimum, and then increases with increasing particle concentration. Because the suspensions are sterically stabilized under the conditions where the particle surfaces are fully covered with by a thick layer of adsorbed polymer, the viscosity decrease can be attributed to the reduction of network density in solution. But under the low coverage conditions, the particles are flocculated by bridging and this leads to a viscosity increase with shear-thinning profiles. The polymer chains with high molecular weights form flexible bridges between particles. The stress-dependent curve of storage modulus measured by a stress amplitude sweep shows an increase prior to a drastic drop due to structural breakdown. The increase in elastic responses may arise from the restoring forces of extended bridges with high deformability. The effect of PEO on the rheological behavior of silica suspensions can be explained by a combination of concentration reduction of polymer in solution and flocculation by bridging.  相似文献   

17.
This paper presents results on the rheological behaviour of suspensions of two kinds of TiO2 particles in two different polymer solutions. The particles differ in their hydrophilic or hydrophobic properties. The dispersing media are a solution of high molecular weight polyisobutylene in decalin and a solution of a low molecular weight polybutene in decalin. The concentrations of polymer are adjusted in order to get the same zero shear viscosity. The shear viscosity measurements display an apparent yield stress in some cases. The existence and the values of the yield stress depend on the volume fraction of solid particles and on the type of particles. The evolution of the intrinsic viscosity and of the maximum packing fraction vs the shear rate is interpreted in terms of evolution of the size and of the shape of aggregates of particles under shear. The effect of temperature on the development of the yield stress is also discussed. The results are completed by microscopic observations.  相似文献   

18.
The viscosity of material is considered at propagating crack-tip. Under the assumption that the artificial viscosity coefficient is in inverse proportion to power law of the plastic strain rate, an elastic-viscoplastic asymptotic analysis is carried out for moving crack-tip fields in power-hardening materials under plane-strain condition. A continuous solution is obtained containing no discontinuities. The variations of numerical solution are discussed for mode I crack according to each parameter. It is shown that stress and strain both possess exponential singularity. The elasticity, plasticity and viscosity of material at crack-tip only can be matched reasonably under linear-hardening condition. And the tip field contains no elastic unloading zone for mode I crack. It approaches the limiting case, crack-tip is under ultra-viscose situation and energy accumulates, crack-tip begins to propagate under different compression situations.  相似文献   

19.
The viscosity of material is considered at propagating crack-tip. Under the assumption that the artificial viscosity coefficient is in inverse proportion to power law of the plastic strain rate, an elastic-viscoplastic asymptotic analysis is carried out for moving crack-tip fields in power-hardening materials under plane-strain condition. A continuous solution is obtained containing no discontinuities. The variations of numerical solution are discussed for mode Ⅰ crack according to each parameter. It is shown that stress and strain both possess exponential singularity. The elasticity, plasticity and viscosity of material at crack-tip only can be matched reasonably under linear-hardening condition. And the tip field contains no elastic unloading zone for mode Ⅰ crack. It approaches the limiting case, crack-tip is under ultra-viscose situation and energy accumulates, crack-tip begins to propagate under different compression situations.  相似文献   

20.
压-剪混合型定常扩展裂纹尖端的弹黏塑性场   总被引:3,自引:2,他引:1  
梁文彦  王振清  周博 《力学学报》2006,38(5):618-625
假定黏性系数与塑性等效应变率的幂次成反比,考虑其黏性和裂纹面摩擦接触效应 建立了压-剪混合型定常扩展裂纹尖端弹黏塑性场的渐近方程,求得了裂纹尖端场不含应力、应变间 断的数值解. 并讨论了压-剪混合型裂纹数值解随各个参数的变化规律,计算结果 和分析表明,压-剪混合型裂纹尖端场是满塑性的,不含有弹性卸载区,黏性效应是研究扩展裂纹尖端场时的一个重要因素. 无论混合裂纹趋近I型还是趋近II型,静水压力随摩擦系数的增加都是增加的,裂纹面摩擦 效应是阻止裂纹扩展速度的因素,且摩擦作用越强,裂纹尖端场的韧性越高.  相似文献   

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