【作者】 蒋继乐；

【导师】 孟永钢；

【作者基本信息】 清华大学 ， 机械工程， 2012， 博士

【摘要】 摩擦现象广泛存在于机械结构中，针对不同需求实现增摩、减磨和摩擦主动控制是机械设计重要的目标之一。基于外场控制摩擦是实现摩擦主动控制的重要途径。电/磁流变智能材料因其强度在外场调控下可实现2~5个数量级的增强而成为摩擦主动控制的研究热点。研究电/磁流变效应的机理，讨论颗粒结构与强度的关系对电/磁流变器件设计及应用具有重要意义。本文从颗粒间摩擦与润滑的角度对电/磁流变效应的机理进行了研究。首先，根据不同材料的电流变液的剪切流变特性，提出了一种新的结构参数。利用这一结构参数，对不同体积比例的基于沸石/硅油的电流变液在恒定电场、变剪切速率模式下的流变曲线归一化，得到了曲线形式和物理意义与摩擦学中常用的Stribeck曲线具有良好对应关系的归一化曲线。进而借鉴摩擦润滑状态分析了电流变液剪切过程中颗粒结构变化、颗粒-极板的相互作用以及剪切应力的来源。结合电流变液在低剪切速率下的剪切增稠现象，应用特征值分别为10-6、10-4、10-2的结构参数将沸石/硅油基的电流变液颗粒结构随剪切速率增大的演化过程划分为：初始链结构状态、剪切增稠结构状态、过渡结构状态、剪切流挤压结构状态。然后，在自制的磁流变剪切装置上发现并研究磁流变液剪切过程中的粘滑现象。根据粘滑空间周期，估算出低剪切速率下磁流变液的剪切屈服区域位于颗粒结构与极板的界面处，并用视频观测进行了验证。分别用电流测试与声发射测试技术对电/磁流变液剪切过程中颗粒结构变化进行辅助表征。电流测试结果印证了基于结构参数对电流变液剪切状态的划分；声发射信号的特征频率成分和杂散峰强度随外加磁场强度和剪切速率的升高而降低，反映了颗粒-极板的碰撞情况。进而，通过改变极板粗糙度与基础液润滑性能讨论界面性质对磁流变效应的影响。实验发现增大粗糙度和提高基础液的润滑性能会降低磁流变液剪切强度，并阻碍粘滑现象产生。粗糙度对局部磁感应强度的调制和对颗粒结构的破坏降低了剪切强度并影响粘滑现象的产生；颗粒-极板或颗粒间润滑性能增强降低了颗粒结构强度以及颗粒-极板之间的相互作用势，最终也影响了剪切强度。最后，对基于电流变效应的摩擦控制器件的极板表面覆盖尼龙网格，改变极板处局部电场强度以及极板与颗粒结构相互作用势；对磁流变离合器剪切元件进行波纹状设计，强化局部磁感应强度。试制并测试器件，最终获得器件性能增强。更多还原

【Abstract】 Friction exists in all machines. Controlling the friction, either increasing orreducing, is crucial in modern machine design. Friction control based on external fieldsis one of the important methods. The large range of shear resistance modulation in2~5orders of magnitude upon the external electro/magnetic field of electrorheological(ER)/magnetorheological (MR) fluids implies great potential in such applications. Abetter understanding of the mechanism of ER/MR effect is very important for improvingthe performance of the devices. The mechanism of ER/MR effect has been researched inthis study based on the view point of tribology.First a new structure parameter is proposed according to the shear behavior of ERfluids of different materials. This parameter can be used to normalize the shear curves ofER fluids based on zeolite/silicone oil under constant electric field and ramped shearrate, resulting in a curve being analog to Stribeck curve, not only in shape, but also inphysics. So the lubrication regime defined in tribology has been introduced to theanalysis of structure revolution of ER fluids during the shearing, especially theinteraction between the aggregates of particles and the shearing plates along with thesource of the shear resistance in ER effect. In addition the shear thickening of ER fluidsunder low shear rates has been discussed. The magnitude of the critical structureparameters when the shear thickening occurs are all approximately10-6. Together withthe characteristic structure parameter values,10-4and10-2, the particle structureevolution of zeolite/silicone oil based ER fluids can be classified into four states: initialchain state; shear-thickening enhanced structure state; transition structure state and flowcompressed structure state.The stick-slip behavior of MR fluids below the shear rates of1s-1has beenresearched on a self-made MR shear test rig with uniform nominal shear rate. Based onthe observed spatial period of the stick-slip phenomenon it is speculated that the shearyield region locates in the boundary between the aggregates of particles and theshearing plates. The particles involved in the yield region are much fewer comparing tothe whole aggregates, most of which maintain a tetragonal chain structure perpendicularto the plates during shearing process. The images recorded during the shear process provided evidence to this speculation. The current test and acoustic emissionmeasurements are introduced to the ER and MR test. The variation of electric currentduring the shearing verifies the regime classification of shear curves based on theproposed structure parameter. The characteristic frequency component of acousticemission signals during the shearing of MR fluids decreases with the increase of themagnetic field strength and the shear rate, indicating the evolution of theaggregates-plates interaction.Then the influence of the boundary properties to MR effect is studied by changingthe roughness of the shear plates and lubrication ability of base oils. It has been foundthat the shear strength of MR fluids decreases with the increase of the surface roughnessand the improvement of the lubrication ability of its base oil. The stick-slip behavior ofthe MR fluids is diminished once the shear plates with higher surface roughness or thebase oil with better lubrication ability is used.Finally the prototypes of active friction control based on ER and MR effect aredesigned and tested, respectively. In order to enhance the local field and the interactionbetween the aggregates of particles and plates, the surfaces of ER device are coveredwith nylon textiles, while the boundary of MR clutch main part is modified with waveform boundary. Both of the two modifications show the improvement of theperformance of the device.更多还原