Collaborative Research: Size Effects on Magneto-Mechanics of Ni-Mn-Ga Fibers

合作研究：Ni-Mn-Ga 纤维磁力学的尺寸效应

• 批准号: 1207282
• 负责人: David Dunand
• 金额: $ 34.71万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-15 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1207282&HistoricalAwards=false
• 关键词: Collaborative; Research; Size; Effects; Magneto

TECHNICAL SUMMARY:This project lays the foundation for a new class of active materials - magnetic shape-memory fibers with tailored geometry, microstructure and magneto-mechanical properties - to be used as transducers for micro-devices and as building blocks for composites or cellular structures. Magnetic-field-induced twinning is responsible for the high magnetoplastic strains achievable in monocrystalline Ni-Mn-Ga. By contrast, polycrystalline Ni-Mn-Ga shows no magnetoplasticity because twinning is inhibited by internal incompatibility stresses developed between adjacent, misoriented grains. The PIs recently discovered that porosity, because it reduces internal stresses, allows twinning to occur in polycrystalline Ni-Mn-Ga foams, resulting in magnetoplastic strains in the foam struts. Applying this concept to individual fibers, our hypothesis is that tailored grain size (with respect to fiber size) and grain orientations will allow tuning the magnetoplastic strain from polycrystalline (0%) to monocrystalline (~10%) behavior.In this basic study, we will develop a fundamental understanding of how fiber geometry and grain microstructure enable magnetic-field-induced strains in polycrystalline Ni-Mn-Ga fibers, leading to experimentally-validated models that can quantitatively predict the magnitude of magnetoplastic strain for a given fiber structure. Fundamental experimental and theoretical studies probing the mechanisms responsible for magnetoplasticity in the fibers will be carried out. First, the fiber geometry will be varied, in terms of cross-sectional shape and diameter, by using two versatile manufacturing methods (Taylor wire drawing and melt extraction). Then, the fiber grain size and texture will be tailored: the ratio of grain to fiber diameter will be varied from 1 (polycrystalline fiber) to ~1 (bamboo structure) and compared to single-crystal fibers; grain orientation will be varied from random to fiber texture. Third, the magneto-mechanical properties of the fibers will be characterized and numerically modeled on two length scales: (i) at a shorter length scale, models based on the mutual interaction of twinning dislocations and dislocation-interface interactions will predict the effect of free surfaces on the constitutive behavior of Ni-Mn-Ga in small volumes; (ii) at larger length scale, finite-element models will predict, based on the constitutive behavior, the magneto-mechanical behavior of an assembly of bamboo grains within a fiber. Collaborators will embed fibers in polymer matrix to create composites to study their magneto-mechanical properties, or create fiber bundles to study their magneto-caloric properties.NON-TECHNICAL SUMMARY:The present project is a coupled experimental-theoretical study of the magneto-mechanics of magnetic shape-memory fibers, a novel class of materials. It focuses on identifying, quantifying and predicting the effects of fiber geometry and grain microstructure upon reduction of internal stresses and the resulting enhancement in magnetoplastic strain, a phenomenon recently demonstrated in struts of foams by the PIs. The results obtained will be general in nature and thus applicable not only to Ni-Mn-Ga but also to the whole class of magnetic shape-memory alloys.Ni-Mn-Ga fibers with tailored grain structures are expected to show large magnetoplastic strain (i.e. they deform when exposed to a variable magnetic field) which are much higher than magnetostrictive material containing strategic rare-earth elements. These Ni-Mn-Ga fibers may be implemented without further processing in smart actuators and may thus grow rapidly in industrial importance, resulting in a transformative effect on various sensor and actuator technologies including bio-medical pumps, ink-jet printer valves, power-generation transducers, and haptics devices. Beyond sensor and actuator applications, fibers and fiber constructs may enable new applications such as efficient magnetic cooling devices with high heat-transfer rates due to their large specific areas. This project will educate two graduate students and several undergraduate students, whose recruitment will emphasize women and minorities. Beside research, the students will participate in various outreach activities using the shape-memory materials to introduce materials science and technology to young women, minorities, and grade school (K-12) students. This project will leverage collaboration with four international partners (in Europe and Asia) thereby generating high visibility and impact. The recent results of the PIs resonated strongly with the scientific community and were highlighted in national media. These contacts will be leveraged for disseminating results of the proposed project. The PIs have submitted two patents and pursue a spin-off project for transitioning the field to the US high-technology industry.

技术摘要：该项目奠定了新型活性材料的基础 - 具有量身定制的几何形状，微观结构和磁机械性能的磁性 - 记忆纤维 - 可用作微设备的传感器，作为复合材料或细胞结构的构建块。磁场诱导的双胞胎负责单晶Ni-Mn-GA可以实现的高磁塑料菌株。相比之下，多晶Ni-Mn-GA没有磁性塑性性，因为双胞胎受到内部不兼容应力的抑制，相邻的，不良的晶粒之间产生的内部不兼容应力。 PIS最近发现，孔隙率降低了内部应力，因此可以在多晶Ni-Mn-GA泡沫中进行双胞胎，从而导致泡沫支柱中的磁性菌株。 Applying this concept to individual fibers, our hypothesis is that tailored grain size (with respect to fiber size) and grain orientations will allow tuning the magnetoplastic strain from polycrystalline (0%) to monocrystalline (~10%) behavior.In this basic study, we will develop a fundamental understanding of how fiber geometry and grain microstructure enable magnetic-field-induced strains in polycrystalline Ni-Mn-Ga纤维，导致实验验证的模型，可以定量预测给定的纤维结构的磁塑料菌株的大小。 将进行基本的实验和理论研究，探测负责纤维中磁性磁性的机制。 首先，通过使用两种多功能制造方法（Taylor电线图和融化提取），将纤维几何形状在横截面形状和直径方面变化。 然后，将量身定制纤维晶粒尺寸和纹理：晶粒与直径的比率将从1（多晶纤维）变化到〜1（竹结构），并将其与单晶纤维相比；晶粒方向将从随机到纤维质地变化。第三，将在两个长度尺度上对纤维的磁力机械性能进行表征，并在数值上进行建模：（i）基于较短的长度比例，基于双胞胎脱位和脱位交互的相互相互作用的模型将预测自由表面对小体积ni-mn-ga的本质性行为的影响； （ii）在较大长度的规模上，有限元模型将根据构成行为预测纤维内竹晶粒组装的磁力机械行为。 合作者将嵌入聚合物矩阵中的纤维以创建复合材料来研究其磁机电特性，或者创建纤维捆绑包以研究其磁性含量的属性。Non-Technical摘要：本项目是一项耦合的实验性研究，对磁性形状 - 纤维纤维的磁性磁化型磁性材料的实验性研究。 它着重于识别，量化和预测纤维几何形状和晶粒微观结构对减少内部应力的影响以及磁性塑料菌株的增强，这一现象最近通过PIS在泡沫支柱中证明了这一现象。获得的结果本质上是一般性的，因此不仅适用于Ni-MN-GA，而且适用于整个磁性形状 - 内存合金。具有量身定制的晶粒结构的Ni-MN-GA纤维有望显示出较大的磁性塑性菌株（即，在暴露于可变磁场时它们会变形），这些磁场在可变的磁场时），这些磁场比具有磁性材料的较高材料具有较高的材料较高的策略性策略性，而这些磁场均高得多。 这些Ni-MN-GA纤维可以在不进一步处理智能执行器中实施，因此可能会在工业重要性上迅速增长，从而对包括生物射手泵，印刷打印机，功率生成传感器以及HAPTECICES设备在内的各种传感器和执行器技术产生变革性的影响。除了传感器和执行器应用之外，纤维和纤维构建体还可以实现新的应用，例如由于其较大的特定区域，具有高热量速率的有效磁化设备。 该项目将教育两名研究生和几名本科生，他们的招聘将强调妇女和少数民族。除研究外，学生还将使用形状记忆材料参加各种外展活动，向年轻妇女，少数民族和小学（K-12）学生介绍材料科学和技术。该项目将利用与四个国际合作伙伴（在欧洲和亚洲）的合作，从而产生很高的知名度和影响力。 PI的最新结果引起了科学界的强烈共鸣，并在国家媒体中得到了强调。这些联系将被利用以传播拟议项目的结果。 PI已提交了两项专利，并从事衍生项目，以将该领域转移到美国高科技行业。