Fatigue of Nickel MEMS Structures

该补助金旨在从根本上了解LIGA方法生产的纯多晶镍MEMS结构中疲劳裂纹萌生和生长的微观机制。使用扫描和透射电子显微镜技术的微观结构的接收和热处理的镍MEMS结构进行了研究。初始的表面拓扑结构，其特征在于与原子力显微镜。单调和循环变形实验被用来确定镍MEMS结构的本构行为。微弯曲实验测量塑性长度尺度，用于随后的变形建模。通过扫描和透射电子显微镜阐明与此长度尺度的微观结构和亚结构特征。光滑（抛光和未抛光）试样的疲劳寿命作为应力范围和平均应力的函数进行了研究。初始样本连续变形至失效，以确定失效循环次数。然而，随后的实验将停止在不同部分的测量周期数失败，以促进表面拓扑结构（原子力显微镜），微观纹理（取向成像显微镜）和损坏（扫描和透射电子显微镜）的增量表征。在高中阶段，P.I.将与普林斯顿高中的一个高年级学生互动，这个项目旨在让学生接触令人兴奋的MEMS技术。在本科阶段，由普林斯顿工作/学习计划（每年）资助的两名少数民族本科生将在常规学年期间从事拟议的计划。另外两名来自其他机构的本科生（每年）将在夏季被雇用从事该项目，由NSF REU资金支持。从实验中获得的基本理解将指导基于机理的模型的开发，用于预测疲劳裂纹的萌生和扩展。该模型的影响将探讨镍MEMS结构的损伤容限设计。私家侦探将开发一个新的研究生课程的MEMS结构，包括MEMS制造的基础，微观结构，纹理，物理/机械性能和设备的考虑。课程的摘要和笔记将在全球网络上免费提供给全球观众。***

This grant is aimed at a fundamental understanding of the micromechanisms of fatigue crack initiation and growth in pure polycrystalline nickel MEMS structures produced by the LIGA method. The microstructures of the as-received and heat-treated nickel MEMS structures are studied using scanning and transmission electron microscopy techniques. The initial surface topologies are characterized with atomic force microscopy. Monotonic and cyclic deformation experiments are used to determine the constitutive behavior of the nickel MEMS structures. Micro-bending experiments measure the plasticity length scale for the subsequent modeling of deformation. Microstructural and substructural features associated with this length scale are elucidated via scanning and transmission electron microscopy. The fatigue lives of smooth (polished and unpolished) specimens are studied as functions of stress range and mean stress. The initial specimens are deformed continuously to failure to determine the number of cycles to failure. However, subsequent experiments will be stopped at different fractions of the measured number of cycles to failure to facilitate the incremental characterization of surface topology (atomic force microscopy), micro-texture (orientation imaging microscopy), and damage (scanning and transmission electron microscopy). At the senior high school level, the P.I. will interact with a senior class in a Princeton High School in a program designed to expose students to exciting MEMS technology. At the undergraduate level, two minority undergraduate students funded by the Princeton work/study program (per year) will work on the proposed program during the regular academic year,. Two additional undergraduate students (per year) from other institutions will be hired to work on the project during the summer, supported by NSF REU funds. %%%The fundamental understanding gained from the experiments will guide the development of mechanism-based models for the prediction of fatigue crack initiation and growth. The implications of the models will be explored for damage tolerant design of Ni MEMS structures. The P.I. will develop a new graduate course on MEMS structures, including the fundamentals of MEMS fabrication, microstructures, textures, physical/ mechanical properties and device considerations. Overheads and notes from the class will be made freely available to the global audience on the worldwide web. ***