【作者】 苗运江；

【导师】 杨志伊；

【作者基本信息】 中国矿业大学 ， 机械设计及理论， 2009， 博士

【摘要】 磁流变液是一种对磁场敏感的智能材料,是由磁性颗粒、基液和表面活性剂组成的混合液。磁场显著影响磁流变液的流变性,在无外磁场作用时,磁流变液呈现出液体性质,具有良好的流动性;有外磁场作用下,磁流变液的表观粘度增大,甚至失去流动性,呈现出固体的性质;而磁场消失后迅速恢复原来的流动性,这种变化是可逆的、连续的,而且磁流变液的性能受温度变化影响较小。磁流变液的一个主要性能指标是屈服应力,当外加应力小于屈服应力时磁流变液呈现固体的性质,大于屈服应力时磁流变液开始流动,呈现出流体的性质。由于磁流变液的许多理论问题还在探讨之中,关于磁流变液的流变性能变化机理研究,磁场中磁流变液结构的运动变化规律,磁流变液的制造与生产,性能测试和设计标准、磁流变液元器件的控制理论与技术等方面有很多待解决的问题,目前磁流变液技术还远未达到大规模应用的阶段。该论文介绍了磁流变技术及其器件开发的现状和发展趋势,论述了磁流变效应的流变机理和模型描述,分析了软启动技术的现状,讨论了将磁流变技术引入传动工程领域的重要性,提出了研究目的及研究内容。该论文通过对磁性颗粒、基液和表面活性剂的选择,用颗粒平均直径为2.5um的羰基铁粉制备了体积浓度为57.9%、36.2%、26.7%和19.6%四种性能良好的磁流变液,用颗粒平均直径为3.5um的羰基铁粉制备了体积浓度为57.9%的磁流变液。将磁颗粒看成是外磁场中的磁偶极子,以磁偶极子理论从理论上分析了磁吸引力、重力、Van der Waals力、分散剂的排斥力对磁流变液稳定性的影响,分析结果说明重力场是导致磁颗粒沉降的最关键因素,分散剂的排斥力是抵抗磁吸引力和Van der Waals力保证磁颗粒不团聚成块的关键因素,想制备出不沉降的低浓度MRF是不可能的。该论文中制作提拉式磁流变液屈服应力测试装置,用铜、铝和钢等不同材料制作了分别具有1mm/2mm槽深的矩齿形/三角形表面形貌的提拉块,测量了不同材料不同表面形貌的提拉块屈服应力与磁场的关系,观测到壁面滑移与磁场强度、表面形貌和耦合材料有关,其中耦合材料的磁化率是最重要的,低磁化率材料制作的耦合面在强磁场中都会产生壁面滑移,高磁化度材料制作的壁面无论如何光滑都不会发生壁面滑移。实验证明耦合面间距对屈服应力的测量结果有重大影响。该论文提出了用阻抗法测量磁流变效应的方法,并用阻抗法测量了磁流变液的响应过程,观测到磁流变效应的发生是一个渐变的过程,当磁场强度大于某临界点后,磁流变效应在数毫秒内迅速响应,然后逐渐增强,但即使超过数百毫秒响应过程也没有结束,不同体积浓度的磁流变液响应过程类似。实验证明MRF是一种粘弹性体。该论文根据Bingham模型设计制作了一种大功率的剪切工作模式下的磁流变液软启动装置,并进行了静态性能和模拟软启动过程及小滑差工况下的温升的测试,实验证明这种装置传递力矩大,可以作为大功率传动装置的离合器,在滑差转速为10rpm工况下温升不超过密封材料的允许值,可以作为多电机驱动的功率分配装置,但作为软启动装置的启动过程不能超过30秒。更多还原

【Abstract】 Magnetorheological fluid (MRF) is one kind of smart material that is sensitive to magnetic field. MRF is a mixture liquid consisting of magnetic granules, base fluid and surfactant. Magnetic field remarkablely effects on rheological behavior of MRF. Without external magnetic field, magnetorheological fluid flows well that shows liquid properties. The apparent viscosity of MRF augments and some solid properties present, becomeing dense even losing its fluidity, if an external magnetic field is applied. It resumes its fluidity rapidly and this change is reversible and continuous when external magnetic field is removed. Furthermore, its performance is independent to temperature.One key performance of magnetorheological fluid is yield stress. When the external stress is less than yield stress, magnetorheological fluid shows the solid properties; While the stress is bigger than yield stress, it begins to flow and shows liquid properties.Because many theoretic issues are still in discussion, there are many questions to be solved about its rheological behavior changing mechanism, its frame variation laws in magnetic field, its manufacture and yield, performance testing, design standard and its element control theory and technology, etc. This technology has not yet been widely used at the present time.This paper introduces the present state and trend of development of MRF, MRF devices and MRF technology at first. Then rheological behavior changing mechanism and its models are discussed. The present state of soft-start and the significance of MRF introducing into transmission engineering field are analysed thirdly. Finally, the goals and contents of this dissertation have been put forward briefly.Through selecting magnetic granules, based liquid and surfactant, good performance magnetorheological fluid is prepared. Four MRF are prepared with carbonyl iron, which volume percent are 57.9%, 36.2%, 26.7% and19.6%, using average diameter 2.5um granules. And 57.9 volume percent MRF with 3.5 um carbonyl iron powder is prepared, either. The magnetic particles can be regarded as dipoles. The influnce factors on stability of MRF is analysed using magnetic dipole theory, which are magnetic force, gravity, Van. Der Waals, exclusive force from dispersant. It illuminates that the key factor causing magnetic granules deposit is gravity field. The exclusive force from dispersant is the key factor that prevents magnetic granules reunites together by magnetic force and Van. Der Waals. It’s impossible to preparat never subsideing MRF.A pulling testing instrument measureing yield stress of MRF is manufactured. Different materials, copper, aluminium, steel, and different pulling sheets grooved with 1mm/2mm, rectangular/triangular roughness are maked. The relationship between yield stress and magnetic field strength with these diffent sheets are tested.It observed that wall effect is related to magnetic field strength, surface roughness and coupling material. The coupling material is the most important. Wall effect occurs if the couplings are made in non-magnetoconductivity material and the magnetic field is strong enough. While wall effect doesn’t occur if the couplings are made in magnetoconductivity material, whether how smooth the surface is.The response process is tested by measureing the resistance of MRF in magnetic field. It shows that the magnetorheological effect is gradual changing. When it reaches the critical point, magnetorheological effect response within milliseconds, then buildups gradually. It doesn’t stop even 1000 milliseconds passed. Different volume percent MRF have similar response process. The experiments prove that MRF is a viscoelastic body.A sheer mode high-power MRF soft-start device was manufactured based on Bingham model and its static performances are measured. The temperature rises when rotate speed difference being 10 rpm and emulated soft-start process are tested. The experiments prove that the device can transfer huge moment, equilibrate the power among motors. But the soft-start process can’t exceed 30seconds.更多还原