【作者】 范艳层；

【导师】 龚兴龙； 宣守虎；

【作者基本信息】 中国科学技术大学 ， 固体力学， 2013， 博士

【摘要】 磁流变弹性体是一种磁敏智能材料,它主要由微米级的软磁性颗粒和高分子聚合物弹性基体组成。在外磁场的作用下,颗粒在基体内形成链状结构或者复杂的三维结构,其流变性能或机械性能在外界磁场的作用下发生连续、快速、可逆的变化。这些独特的性能使其受到众多的关注,并且在减振、降噪等领域具有广泛的应用前景。在磁流变弹性体领域,以往的研究热点主要集中在模量方面,然而对工程应用有重要影响的阻尼性能却一直未得到应有的关注。对于自调谐式吸振器,低阻尼的磁流变弹性体会增强其吸振效果；而对于隔振器,当激励频率处于系统的不同频段时,则需要阻尼可调的磁流变弹性体才能够使其达到良好的隔振效果,即要求磁流变弹性体的阻尼具有可控性。但是,目前磁流变弹性体中普遍存在阻尼过大、阻尼可控性能较差等问题。因此,为了使磁流变弹性体器械获得理想的减振效果,研究磁流变弹性体的阻尼性能是非常具有实用价值和科学意义的。针对上述问题,本文选择性能优良的顺丁橡胶作为基体,系统地研究了顺丁橡胶基磁流变弹性体的制备方法及力学性能。以研制出实用型的磁流变弹性体为目标,对材料的界面和基体进行了设计和改良,实现了磁流变弹性体阻尼性能的优化和调控。具体内容如下：1.基于界面对材料性能有十分显著的影响,本文对磁流变弹性体的界面摩擦阻尼性能进行了研究。利用不同粒径的羰基铁粉制备出具有不同界面特性的样品,研究了不同磁场及应变条件下磁流变弹性体的阻尼性能。首次提出磁流变弹性体的界面摩擦阻尼主要来自自由橡胶和磁性颗粒之间的界面滑移。该研究结果对进一步建立磁流变弹性体内部界面的理论模型具有一定的指导作用。2.为了优化磁流变弹性体的阻尼性能,研制出具有低阻尼的材料,本文对磁流变弹性体的界面和基体进行了优化和设计。首先选择马来酸酐作为相容剂来改善两相间较差的界面状况。研究发现马来酸酐的添加可以有效地增强颗粒与基体之间的相容性,在降低磁流变弹性体损耗因子的同时,还增强了其储能模量和拉伸强度,但是磁流变效应却有所下降。此外,磁流变弹性体的基体材料也是其阻尼的来源之一,采用石墨烯纳米片作为基体的增强相,制备出了不同石墨烯纳米片含量的磁流变弹性体,并对其损耗因子、模量、拉伸强度及热扩散率等性能进行了测试和分析。系统地研究了在不同应变、磁场及温度下石墨烯纳米片对阻尼性能的影响,发现石墨烯纳米片通过阻碍基体分子链的运动,有效地降低了磁流变弹性体的阻尼。上述两种方法(改善界面状况和增强基体)为降低磁流变弹性体阻尼提供了理想的方案,对实际应用中的磁流变弹性体吸振器有着非常重要的意义。3.本文对磁流变弹性体的阻尼可控性能展开了一系列的相关研究。系统研究了基体的交联密度对磁流变弹性体阻尼可控性能的影响。发现基体的交联密度可直接影响阻尼的可控性能。当基体的交联密度较低时,增塑剂和频率对阻尼可控性能的影响非常显著。此外,低的基体交联密度使磁致模量和磁流变效应也得到了增强。针对上述现象,首次提出颗粒重排是实现磁流变弹性体阻尼可控的关键因素。基于以上提出的阻尼可控机理,研究了温控材料对阻尼可控性能的影响。以聚己内酯作为一种温度可控元素添加到顺丁橡胶基体中,研制出了一种新型的阻尼可控的磁流变弹性体。发现通过改变聚己内酯的含量、温度以及外加磁场,可有效控制磁流变弹性体的阻尼性能。实现磁流变弹性体的阻尼可控对工程器械(如隔振器)的性能有着极其重要的影响,上述研究结果将有望极大地促进磁流变弹性体在该领域的应用。更多还原

【Abstract】 Magnetorheological elastomers (MREs) are a kind of magneto-sensitive materials, which are composed of microsized soft magnetic particles and low-permeability elastomers materials. During the preparation, the particles form an anisotropic ordered pre-configuration such as chains or more complex three-dimensional structures under applying a magnetic field. It is noted that the rheo logical or mechanical properties can be changed continuously, rapidly and reversibly by an external magnetic field. Based on these unique characteristics, MREs have attracted increasing attention and have been considered for a wide range of applications in vibration reduction and noise reduction, etc.Tremendous efforts have been devoted to the modulus of MREs in the past ten years, while the damping properties which are very important in practical application have not attracted considerable attention. For MRE-based vibration absorbers, low damping will contribute to the vibration reduction. Furthermore, for MRE-based vibration isolators, the tunable damping is preferred for vibration reduction effect when the excitation signal is located in different resonance frequency bands of the system. However, the high and uncontrollable damping is detrimental to some applications of MREs. Therefore, to develop high-efficiency MRE-based vibration reduction devices, it is very practical and important to study the damping properties.To overcome the above-mentioned problems, cis-polybutadiene rubber (BR) was used as matrix. The corresponding fabrication processes were studied to prepare BR based MREs and their mechanical properties were also investigated. In order to optimize the damping properties and obtain the practical MREs, the interface and the matrix of MREs were designed and improved. Details are described as following:1. The effect of interface between the two phases on the mechanical performances of the material is very important. In this study, the interfacial friction damping properties of MREs were investigated experimentally by using two kinds of carbonyl iron particles. The damping properties of MREs were measured under different magnetic fields and different shear strain amplitudes. The results demonstrated that the interfacial friction damping mainly comes from the frictional sliding at the interfaces between the free rubber and the particles, which is guidable for establishing interfacial model of MREs. 2. The interface and elastic matrix need to be improved to obtain the MREs with low damping. Maleic anhydride (MA) was selected as the compatibilizer to modify the interfaces of MREs. The experimental results indicated that the compatibility between the magnetic particles and rubber matrix was enhanced with the increase of MA. The enhancement of the bond between two phases led to different mechanical properties:the reduction of the loss factor, the increase of shear storage modulus, the enhancement of the tensile strength, and the reduction of the MR effect. In MREs, the matrix also plays a very significant role in damping properties. The graphite nanoplatelet (GNP) was selected as the reinforced component in the BR based MREs and their damping properties were investigated. MREs with different contents of GNP were prepared and the mechanical performances including loss factor, modulus, tensile strength and thermal diffusivity were measured. The effect of GNP on the damping properties under different shear strain amplitudes, magnetic fields and temperatures was studied. The results indicated that the flaky GNP could obstruct the sliding friction between the matrix molecular chains. The reinforcement of the matrix resulted in the reduction of loss factor. Consequently, the above methods were hopeful to optimize and reduce the damping of MREs, and helpful for practical application in MRE vibration absorbers.3. The controllable damping properties of MREs have also been investigated. The effect of crosslink density of the matrix on the controllable damping properties was firstly studied. The experimental results showed that the crosslink density of the matrix influenced the controllable damping properties of MREs directly. When the crosslink density of the matrix was low, the effect of plasticizer and frequency on the magneto-induced change of loss factor was remarkable. In addition, by reducing crosslink density, the magneto-induced modulus and the relative MR effect increased. A mechanism for the magneto-induced change of loss factor was proposed and the analysis implied that the rearrangement of particles played an important role in controlling the damping properties of MREs. Based on the mechanism of controllable damping properties, the polycaprolactone (PCL) was selected as the temperature-controllable component in the BR matrix and a novel kind of MREs with controllable damping properties was developed. The experimental results showed that the damping properties of the MREs can be controlled by varying the PCL weight ratio, the temperature, and the magnetic field. In practical applications, the effect of MREs with controllable damping properties on the properties of MREs based devices (MRE vibration isolators) is very important. These results will lead them to be widely applied in practical applications.更多还原