【作者】 韩雪冰；

【导师】 王省哲；

【作者基本信息】 兰州大学 ， 固体力学， 2012， 硕士

【摘要】 铁磁形状记忆合金(Ferromagnetic Shape Memory Alloys,简称为FSMAs)且有强铁磁性、大磁致应变、响应频率高、磁控形状记忆效应等优点,是一种极具应用潜力的铁磁性功能材料。针对铁磁形状记忆合金材料在横向磁场和轴向应力场作用下的马氏体变体重取向的力磁耦合行为和大磁致应变输出等行为,本文开展了相关的理论研究和数值模拟。首先我们基于复合材料细观力学Eshelby等效夹杂理论和Mori-Tanaka场平均方法,将铁磁形状记忆合金材料内部马氏体变体重取向过程中长大的马氏体变体看作夹杂相、变小的马氏体变体看作基体相,推导出了铁磁形状记忆合金材料在力磁耦合重取向过程中的总应变表达式。其次根据热力学原理,建立了描述马氏体变体力磁耦合重取向行为的热力学模型,其中提出了一形式简单、相关系数实验可测并具有力学意义的马氏体变体重取向的热力学阻力公式,并由此建立了其与驱动马氏体变体孪晶界移动的广义热力学驱动力间的热力学平衡方程。通过选取适当的描述材料马氏体变体重取向过程中微结构变化的内部状态变量,将细观力学理论与宏观热力学原理结合,实现了对铁磁形状记忆合金材料内部马氏体变体力磁耦合重取向行为的描述。进而模拟了描述材料内部马氏体变体微结构变化的三个内部状态变量及磁化强度的演化过程。相关结果表明：本文的模型可以很好地预测铁磁形状记忆合金马氏体变体发生重取向以及逆取向的相关力磁耦合行为；并可以预测马氏体变体重取向过程发生和结束的临界磁场值及变体逆取向过程发生和结束的临界应力值。最后我们还对马氏体变体重取向过程完全不发生、部分发生和完全发生的机理或外界场限制条件进行了讨论。更多还原

【Abstract】 Ferromagnetic shape memory alloys (FSMAs) are a potential application of ferromagnetic functional material, which exhibit advantages such as high ferromagnetism, huge output strains, high response frequencies etc. The shape memory effect (SME) of FSMAs can be controlled not only by a thermal field or a stress field, but also by a magnetic field. The theoretical studies and numerical simulations for FSMAs are conducted, aiming at their mechanical-magnetic coupling behaviors of martensite variants rearrangement and huge output magnetic field-induced strain behaviors caused by applied both of transversal magnetic field and axial compressive stress.Firstly, the total strain of FSMAs is derived from the Eshelby equivalent inclusion method and the Mori-Tanaka averaged scheme during the martensite variants mechanical-magnetic coupling rearrangement process, by treating the growth variant as inclusion phase and the decrease variant as parent phase. Secondly, the thermodynamic model based on thermodynamic principle is proposed to describe the mechanical-magnetic coupling behaviors during the martensite variants rearrangement process. Furthermore, a simple form thermodynamic resistance formula for martensite variants rearrangement process is proposed, which has the mechanical significant. And the correlation coefficients can be measured by experiment. Thus, a thermodynamic balance equation is established for the thermodynamic resistance formula and the generalized thermodynamic driving force leading to martensite variants twin boundary motion.The proper internal state variables, which combine the micromechanics theory with the thermodynamic principle, are chosen to describe the microstucture change during the martensite variants rearrangement process. The above method realizes to describe the mechanical-magnetic coupling rearrangement behaviors of the martensite variants. The evolution process of the three internal state variables and the magnetization are numerical simulated to describe the microstructure change of martensite variants. The results show that, the model can give the good predictions on the mechanical-magnetic coupling behaviors during the martensite variants rearrangement or inverse rearrangement process of the FSMAs under either the loading of magnetic field or compressive stress. The model can well predict the critical field for the start and end of the martensite variants rearrangement process and the critical stress for the start and end of the inverse rearrangement process. Lastly, the model discusses the mechanism and the applied field conditions of how the martensite variants rearrangement process could not happen, partly happen or completely happen.更多还原