【作者】 金科；

【导师】 郑晓静；

【作者基本信息】 兰州大学 ， 工程力学， 2011， 博士

【摘要】 超磁致仲缩材料由于具有位移大、响应快、驱动简单等性能优势,在智能系统中具有广泛的应用前景,其力学响应行为涉及变形场、磁场、涡流场、温度场相互耦合问题,直接关系到智能系统的性能指标和可靠运行。本论文针对超磁致伸缩材料的非线性多场耦合力学响应进行了理论研究。考虑磁致伸缩材料磁化与外磁场之间的相互作用,建立了磁场-磁化双向耦合的磁性关系,基于热力学原理并结合J-A能量耗散模型考虑了由于不可逆畴壁运动而产生的能量损耗,分析讨论了可逆和不可逆磁化的温度相关性,模拟结果与实验测量数据十分吻合。定量研究发现退磁效应在增大材料磁化难度的同时加剧了磁化过程中的能量损耗,并使未达到饱和的磁致伸缩应变值降低,可以很好的刻画出矫顽场随温度变化的指数衰减规律,以及随预压力增大而增大的趋势。理论研究表明提高温度、降低预压力是降低矫顽场,减少磁致伸缩材料磁滞损耗的有效途径。建立了磁致伸缩材料的磁-弹-热耦合的磁滞本构模型。模型可以定量研究磁致伸缩棒材、膜材在不同磁场、温度场、应力场中的磁化和磁致伸缩行为,并在此基础上着重分析了磁致伸缩薄膜性能对环境温度和面内应力状态的敏感性,研究结果对于提升薄膜的磁致伸缩性能具有重要的指导意义。建立了考虑应力、温度、退磁效应的磁晶各向异性本构模型,针对磁致伸缩Terfenol-D合金,该模型可以很好的刻画出磁晶各向异性对材料宏观磁力行为的影响规律。研究表明,磁晶各向异性主要影响磁化曲线和磁致伸缩应变曲线的非线性区域,增大磁化难度,减缓磁致伸缩应变增涨的速度,同时会减弱不同应力下磁致伸缩曲线的“翻转”趋势。模型指出不同的磁晶各向异性(单轴各向异性、平面各向异性等)并不影响材料磁化强度和磁致伸缩应变的饱和值,只会影响磁化的快慢。在研究磁致伸缩材料在激励磁场下的动态力学响应与材料磁化相互作用的基础上,建立了与频率相关的磁弹性双向耦合的动力学模型,分析讨论了磁滞损耗对磁致伸缩材料动态力学响应的影响。模型可以准确描述实验所揭示的应变回线随激励磁场频率的增大而产生的形状变化和“反转”现象。研究表明磁滞损耗不仅会给制动器的一阶共振频率带来一个向高频的微小漂移,而且使共振振幅产生了与预压力相关的衰减；即使在低频磁场下,磁滞损耗对振幅也有明显的影响。提出一个更加完善的磁弹性耦合理论框架,在此基础上研究了涡电流对磁致伸缩材料磁学性质和力学响应的影响,建立了磁-弹-热-电(涡电流)多物理场耦合的动力学模型,并编写了相应的多重迭代数值模拟程序。定量模拟出磁致伸缩棒在外磁场、应力、温度加载下的共振频率漂移规律：揭示了在不同偏磁场区域内,制动器共振频率的温度敏感性；讨论了涡流损耗产生的热效应对制动器动态力学响应的影响；发现了涡电流产生的热损耗与应力场、磁场密切相关。总之,通过本文的研究,进一步理解了多物理场之间的耦合效应对磁致伸缩材料力学行为的影响,完善了描述磁致伸缩材料磁学、力学性质的理论框架。为解决其它多场耦合问题提供有效的研究思路。对实际工程中磁致伸缩器件的应用奠定了一定的理论基础,为智能系统的设计研发提供了可靠的理论依据。更多还原

【Abstract】 Magnetostrictive materials have an immeasurable applied prospect in smart devices and systems owing to many unique benefits in performance like large displacement, fast response and simple driving. A considerable coupling effect among mechanical field, magnetic field, thermal field, electrical field is therefore being a relevant concern in the applications of magnetostrictive devices. Motivated by the need to promote a more efficient design process and higher performance achievement of development of materials, devices and system designs, this dissertation presents nonlinear modeling of multi-field coupling effects on mechanical behavior of magnetostrictive materials.A thermodynamic framework is constructed to describe the bidirectionally coupled magnetization, and the movement of the domain walls is incorporated to describe hysteresis based on Jiles-Atherton’s model. Furthermore, the temperature dependence of irreversible and reversible magnetization is discussed. The predictions show good correlation with experimental data.It is shown that demagnetization field makes the magnetization hard and increases energy losses, as well as decreases the unsaturation magnetostriction. The coercive field varies with temperature and prestress can be also well described by this work. It is revealed that enhancing temperature and reducing prestress is an effective way to lessen hysteretic losses.A constitutive model which can describe the magneto-thermal-elastic coupling and hysteresis inherent to magnetostrictive materials is proposed. Comparing this model with other existing models in this field, the quantitative results show that the relationships obtained here are more effective to describe the effects of the prestress or in-plane residual stress and ambient temperature on the magnetization or the magnetostriction hysteresis loops for magnetostrictive rods or films.A magnetocrystalline anisotropy model is presented with incorporating the effects of stress, thermal, demagnetization field. The model is validated against experiment measurements made on Terfenol-D alloys. It is shown that magnetocrystalline anisotropy shows a remarkable effect on the magnetization and magnetostriction. With the anisotropy constant increasing, the nonlinear regions of magnetization curves and magnetostrictive curves are enlarged, and magnetization becomes hard. It is also shown that different forms of anisotropy (axially anisotropic, planar anisotropy and cubic anisotropy), which have almost no effects on the saturation value of magnetization and magnetostriction, affect the magnetization processes remarkably. A frequency-dependent bidirectionally coupled magnetoelastic dynamic model is proposed by considering the interaction between mechanical responses with magnetization field. The effects of hysteresis losses on the dynamic behavior of magnetostrictive materials are then discussed. Model predictions show good correlation with experimental data, which demonstrates that the model can well capture the dynamic behavior of magnetostrictive materials. Resonance frequency shifts and amplitude reductions due to hysteresis losses are analyzed. Furthermore, the effects of hysteresis losses on the dynamic vibration behavior in the low frequency range as well as stress and temperature dependence of hysteresis losses are discussed in detail.A multi-field coupled framework is developed to study the electro-magneto-thermal-elastic coupling effects on the dynamic response of magnetostrictive materials. In the model, the influence of thermal effect arising from eddy current is taken into account. A compenhensive description for temperature, pre-stress and bias field dependences of resonance frequency is carried out. Moreover, the effects of eddy current losses on the dynamic behavior of magnetostrictive materials are discussed in detailThese essential and important investigations will be of significant benefit to both the theoretical researches and the applications of magnetostrictive materials in smart or intelligent structures and systems.更多还原