Pattern-Changing Instabilities and Giant Magnetostriction in Periodic Magnetoelastic Composites

这笔赠款的研究目的是阐明具有周期性微结构的磁弹性复合材料中某种类型的“模式变化”不稳定性的影响，以便获得比这些系统中迄今可能的更大的磁致伸缩应变。在纯机械的背景下，众所周知，这些图案变化的不稳定性，其中复合材料中的变形突然从通常的单胞周期图案改变(或分叉)到涉及胞间集体相互作用的新的、较低能量的变形图案，通常与“软”变形模式相关联，其中施加的应力的微小变化可以导致大应变。在早期工作的基础上，将设计理论工具来有效地模拟这些不稳定的可能出现的情况以及复合材料在分叉后的“软”区域中的宏观响应。然后，这些工具将被用于设计磁弹性复合材料，这些复合材料能够产生比迄今可能的显著更大(“巨大”)的磁致伸缩应变。这项研究将产生新颖高效的多场模拟技术，该技术将广泛应用于大类活性材料系统，并将有助于在有限元程序中进行数值实现。在磁弹性复合材料建模和导致大磁致伸缩应变的微结构设计方面的改进应该会在许多工业应用中导致这些材料性能的提高，从汽车悬挂系统中的自适应调谐减振器到机器人工业中的人造肌肉，以及声子和光子带隙开关。这项研究将与教育和外联活动协同进行。

The research objective of this grant is to elucidate the effect of a certain type of "pattern-changing" instabilities in magneto-elastic composites with periodic microstructures in order to achieve much larger magnetostrictive strains than have been possible to date in these systems. In the purely mechanical context, it is known that these pattern-changing instabilities, where the deformation in the composite abruptly changes (or bifurcates) from the usual one-cell periodic pattern to a new, lower energy deformation pattern involving collective interactions between the cells, is typically associated with a "soft" mode of deformation, where small changes in the applied stress can lead to large strains. Building on earlier work, theoretical tools will be designed for modeling efficiently the possible appearance of these instabilities and the macroscopic response of the composite in the post-bifurcation "soft" regime. These tools will then be used to design magneto-elastic composites that are capable of significantly larger ("giant") magnetostrictive strains than have been possible to date. This research will result in novel and highly efficient multi-field modeling techniques, which will be of broad application to large classes of active material systems, and will lend themselves to numerical implementation in FEM codes. Improvements in the modeling of magneto-elastic composites and in the design of microstructures leading to large magnetostrictive strains should lead to enhanced performance of these materials in many industrial applications, ranging from adaptive tuned vibration absorbers in automotive suspension systems to artificial muscles in the robotics industry, as well as phononic and photonic bandgap switches. The research will be conducted synergistically with educational and outreach activities.