【作者】 陈琳；

【导师】 龚兴龙；

【作者基本信息】 中国科学技术大学 ， 固体力学， 2009， 博士

【摘要】 磁流变弹性体是一类智能材料。它是由高分子聚合物和软磁性颗粒组成,在外加磁场的作用下,其模量和阻尼等性能会发生变化。目前已有不少研究者利用磁流变弹性体的变刚度特性,设计了调频式动力吸振器和汽车悬挂轴衬等器件。因此,磁流变弹性体在振动控制等工程领域具有良好的应用前景。磁流变弹性体要实现工程化,一方而需要具备显著的磁流变效应(一般指模量在磁场下的可控范围),另一方面需要具备优异的综合性能。而目前磁流变弹性体的磁流变效应仍不够大,同时多数研究者仅考虑了其模量,忽略了同样重要的阻尼特性和机械性能。在磁流变弹性体机理研究方面,现有模型往往存在过多的假设,影响了结果的可靠性。为解决上述存在问题,本文建立了一套适合于高弹高韧类材料为基体的磁流变掸性体的研制系统,并对磁流变弹性体进行了初步制备;研究了多种制备和测试参数下磁流变弹性体的磁流变效应等力磁耦合性能与机械性能,同时分别通过动态实验和数值模拟的方法研究了磁流变弹性体的阻尼特性;基于观测到的微观结构建立了两种磁流变弹性体的磁致模型;最后根据上述研究成果对材料进行了进一步优化发计,得到了综合性能良好的磁流变弹性体。本文首先概述了磁流变材料的历史、分类和应用,着重介绍了磁流变弹性体的最新研究进展以及存在的科学和应用问题。建立了一套适用于以天然橡胶为代表的高弹高韧类材料为基体的磁流变弹性体的研制系统。在制备基体/颗粒的粘塑态磁性混合物时,分别通过了溶剂法和混炼法两种途径。从性能、工艺、效率和可行性等方面,比较了两种方案的优劣,并最终采用了混炼法。组建了热磁耦合预结构化和固化系统,探索出了基于高弹高韧基体材料的磁流变弹性体的研制方案,并进行了初步制备。实验研究了包括预结构磁场强度、温度、增塑剂和铁粉含量的制备参数和包括动态应变和激励频率的测试参数对磁流变弹性体动态力学性能的影响。此外,搭建了准静态力磁耦合剪切装置,实验研究了不同铁粉含量的磁流变弹性体在有无外场下的准静态应力—应变关系;评估了磁流变弹性体的拉伸强度、撕裂强度、硬度、回弹性、抗热氧老化和耐磨耗性能等基本机械性能。通过扫描电镜观测了不同磁感应强度下制备的磁流变弹性体中磁性颗粒形成的微观结构。发现在预结构过程中施加磁场后,颗粒逐渐团聚成柱状结构。随着施加的磁感应强度的增大,颗粒柱状结构的宽度和长度也随之增大。基于观测到的微观结构,舍弃了袭用于磁流变液的颗粒贯穿模型,建立了适用于磁流变弹性体的力学模型。首先建立了有限柱长模型。在有限柱长模型中,假设磁流变弹性体内包含若干段宽度相同长度随机分布的柱状结构。通过等效磁导率的方法推导出了磁流变弹性体的磁致应力和磁致模量的表达式。接着对磁流变弹性体结构与性能这一问题作了进一步深入的研究。发现对于任何一块磁流变弹性体,其中包含的柱状颗粒结构的长度呈高斯分布。据此建立了一种普遍性更高的磁流变弹性体高斯分布模型。通过该模型研究了颗粒柱结构长度、宽度、外加磁场强度以及应变对磁流变弹性体磁致性能的影响。与传统的Jolly和Davis模型相比,高斯分布模型具有更好的精度和更广的使用范围。分别通过动态实验和数值模拟的方法研究了磁流变弹性体的阻尼特性。相关实验研究结果表明,除刚度可控外,磁流变弹性体也是一种阻尼可控的材料。据此提出了与外加磁场相关的新界面滑移假设。通过对磁流变弹性体取三维代表体积单元,使用有限元软件计算其在受到周期动态剪切应变时的响应。计算结果显示,应力应变的曲线最终收敛于一个迟滞回线。由此计算出了磁流变弹性体的不加磁场时的阻尼比,且比较接近于实验结果。最后基于以上的理论和实验结果,结合应用需求,对磁流变弹性体进行了进一步优化设计。特别是在制备磁流变弹性体时,通过添加适量的炭黑来改性基体性能,可以同时增强磁流变效应,降低损耗因子,以及提高拉伸强度。这对于解决磁流变效应、损耗因子以及机械强度之间的矛盾提供了一种理想方案,对于基于磁流变弹性体设计的调频式动力吸振器有着十分重要的意义。更多还原

【Abstract】 Magnetorheological(MR) elastomers are a class of smart materials.They consist of polymer and soft magnetic particles.Their properties such as modulus and damping can be controlled by an applied magnetic field.MR elastomers have been applied in adaptive tuned vibration absorbers and vehicle suspension bushings because of their controllable stiffness.They will play an important role in the vibration control and other application areas.For engineering application,MR elastomers must own high MR effect(often evaluated by the change of modulus),and other mechanical properties.However,until now,the reported MR effect was not large enough and little research foused on other properties,such as the damping and the mechanical performance.Moreover,current therectical models had too many assumptions to obtain the high accuracy.This dissertation aims to solve the above problems.A fabrication system was established to prepare MR elastomers based on the high-elastic and high-toughness materials.The effects of several basic factors in fabrication and measurement on the properties of MR elastomers were experimentally investigated.Two theoretical models were established according to the microstructure of the MR elastomers. Finally,the MR elastomers were optimized,and high properties were obtained.In the segment of Introduction,the history,classification and application of the MR materials were firstly introduced,and then the recent progresses in MR elastomers were detailed.Besides,the main scientific and applied problems were also pointed out.A fabrication system for MR elastomers based on matrix of the high-elastic and high-toughness materials such as natural rubber was established.To prepare the matrix/particle visco-plastic mixtures,the organic solvent and machine mixing methods were used respectively.By comparing the two options in technology, efficiency and feasibility,the machine mixing method was ultimately perferred. Furthermore,the thermal-magnetic coupled pre-configuration and vulcanization systems were set up,and the scheme for developing MR elastomers based on high-elastic and high-toughness materials was explored.The effects of several basic factors,such as the pre-configuration magnetic flux density and temperature,content of plasticizers and iron particles used in the fabrication and strain amplitude and driving frequency set in the test,on the dynamic properties of MR elastomers were experimentally investigated.In addition,a mechanical-magnetic coupled quasi-static shear mode load device was established. The shear stress-strain relationship of the MR elastomers with different contents of iron particles was obtained under an adjustable magnetic field.The basic mechanical properties concluding tensile and tear strength,hardness,elasticity,thermal-oxidative aging and anti-abrasion performance of MR elastomers were also evaluated according to rubber testing criterion.The microstructure of the MR elastomers prepared under different magnetic flux densities was observed by the scanning electron microscopy.The results indicated that the iron particles gradually aggregated into the cylindrical structure after application of the magnetic field in preparation.As the increment of the magnetic flux density,the length and breadth of the cylindrical structure were both raised.Based on above observed microstructure,a finite-column model which assumed MR elastomers containing several column structures with random length and the same breadth was proposed.Through the effective permeability approach,MR elastomers’ field-induced modulus was derived.Further research on the microstructures and properties of MR elastomers showed that the length of column structures in MR elastomers obeyed the Gaussian distribution.So a Gaussian distribution model was established to study the effects of particle column size,external magnetic field density and shear strain on the field-induced properties of the MR elastomers.The simulation results of the Gaussian distribution model were also compared with other conventional models(such as model respectively proposed by Jolly and Davis) and the relevant published data.Results showed that this model agreed well with the experimental evidence and indeed improved the accuracy on predicting the behavior of the MR elastomers.The damping properties of MR elastomers were studied by the dynamic experiments and the numerical simulations.The experimental results indicated that the MR elastomers were also a kind of controllable damping materials.A method of magnetic field dependent interfacial slipping was proposed to explain the experimental phenomena.After picking the three-dimensional representative volume as a unit model,the stress-strain response was simulated in a dynamic periodic load by using the finite element analysis software ANSYS.The results of stress-strain relationship presented a hysteresis loop.The damping ratio was calcutated from the loop and approached to the previous experimental results.Based on above theoretical and experimental results and combined with the application requirements,the MR elastomers were optimized.It was noted that addition of the carbon black into the matrix resulted in high MR effect,low damping ratio and strong tensile strength.These results were hopeful to solve the extinct shortcoming existing in conventional MR elastomers,and helpful for application in adaptive tuned vibration absorber.更多还原