基于变分原理的单晶NiMnGa合金磁力学行为研究

Single-crystalline NiMnGa alloys can undergo magnetic field-induced strains and possess thermo-elastic shape memory effect, whose unusual properties have attracted wide research interests in the field of smart materials. However, the investigation of this subject is difficult as it involves problems such as multi-field coupling, martensitic variant reorientation and microscopic magnetic domain evolutions. Especially, due to the demagnetization effect, different material points in a NiMnGa specimen exhibit different magneto-mechanical responses, which directly depend on the configuration of the specimen. In this project, the global magneto-mechanical behaviors of NiMnGa specimens will be investigated through the approaches of theoretical modeling, numerical simulations and experimental measurements. The research contents include: (1) Establish the theoretical model through variational approach, considering the effects of twin interface evolution, demagnetization effect, etc.; (2) Design reasonable numerical algorithm and provide accurate simulations on the global magneto-mechanical behaviors of NiMnGa specimens; (3) Conduct systematic experiments on the magneto-mechanical behaviors of NiMnGa specimens under complex loading conditions. The experimental results will be used to verify the accuracies of the numerical simulations; (4) Combining the results of theoretical modeling and experimental measurements, investigate the underlying mechanisms of the global magneto-mechanical behaviors of NiMnGa specimens. The results of the current project will be very important for the developments and applications of single-crystalline NiMnGa products in industries.

单晶NiMnGa合金兼具磁致变形和热弹性形状记忆效应，其独特的磁力学性能已在智能材料领域引起了广泛的研究兴趣。但该课题涉及多场耦合、马氏体变体再取向、微观磁畴演化等诸多问题，具有很大的难度。特别是由于材料的自退磁效应，NiMnGa样品中各点的磁力学响应并不相同，且直接依赖于样品的整体构形。本项目旨在通过理论建模、数值模拟和实验观测等方法，对单晶NiMnGa样品的整体磁力学行为进行系统研究。研究内容包括：(1)通过变分法建立理论模型，其中考虑孪晶界面演化、材料自退磁效应等因素；(2)设计合理数值算法，实现对样品整体磁力学行为的精确模拟；(3)开展复杂磁-力耦合加载实验，系统测量NiMnGa样品的响应数据，对数值模拟的结果进行验证；(4)结合理论模拟和实验测量的结果，深入探讨NiMnGa样品重要行为特征的内在机理。本项目的研究成果对工业领域中单晶NiMnGa产品的开发与应用具有重要意义。

单晶NiMnGa合金是一种典型的磁性形状记忆合金材料，具有独特的材料性能，且已被视为制造新型驱动器和传感器的理想材料，在航天航空、生物医学、自动控制等领域具有广泛的应用前景。本项目针对单晶NiMnGa样品的整体磁力学行为，采用理论建模、数值模拟和实验验证等方法开展了系统的研究工作，已取得的主要研究成果包括：（1）在纯应力加载和磁-力耦合加载条件下，提出了预测单晶NiMnGa样品中孪晶界面成核的准则，完善了描述单晶NiMnGa样品整体磁力学行为的变分法建模方案；（2）基于拓展的材料本构模型研究了单晶NiMnGa样品在旋转磁场中的马氏体变体再取向问题，通过对孪晶界面上构型力的分析揭示了材料磁力学行为特征的内在机理；（3）进一步完善了求解模型控制方程组的数值迭代算法，并开发了耦合有限元边界元算法，有效提高了数值计算的效率；（4）开展了单晶NiMnGa样品的三点弯曲实验和磁场加载弯曲实验，利用DIC等技术观测了样品在各种加载条件下的磁力学响应；（5）建立了适用于有限变形范围的新型板壳理论和面向金属材料的统一多机制连续损伤粘塑性模型，并将应用于后续单晶NiMnGa构件的设计及其在复杂载荷条件下的损伤分析。上述研究成果不仅具有重要的理论价值，而且对后续基于单晶NiMnGa合金的新型智能器件的制造也具有重要意义。本项目的各项研究内容已顺利完成，研究计划和研究目标无变更。