CAREER: Cyclic Plasticity and Fatigue Life of Small-Scale Metal Structures

9876261 vinc本项目在小型金属结构上的两个目标是了解与循环载荷相关的塑性行为，并确定确定低循环和高循环状态下疲劳寿命的机制。循环塑性和疲劳都是根据试样的状态，特别是厚度和微观结构来评估的。测试条件的影响，包括应变率，环境气氛和温度，进行了评估。重点是确定区分独立金属薄膜与大块金属薄膜和粘附在基板上的金属薄膜的行为的关键参数。正在开发的独特设备适合于配备定向成像显微镜单元的环境扫描电子显微镜的标本室。这种布置允许在测试过程中对表面形貌和微观结构进行现场监测。单轴拉伸试样用于简单的测试和分析。金属样品在斯坦福纳米制造设施使用在初步研究中开发的制造技术进行图案化。材料系统包括铝（FCC低熔点金属）、铱（FCC高熔点金属）和钼（BCC高熔点金属）。提高对薄膜力学行为的理解将通过三个途径传递给学生：培养研究生和本科生的研究助理，开发专门的研究生机械行为课程，以及将薄膜力学行为纳入本科课程。基于物理的机械行为模型将允许对设备行为和可靠性进行动态建模，以实现性能优化。受益的技术包括MEMS产品，如高频射频开关和精密电子谐振器。相关的中尺度应用包括用于发电的微型飞机和燃气轮机等设备。这项工作的目标受众包括大学研究人员、设计软件开发人员、小型设备制造商和该技术的最终用户

9876261VinciTwo objectives of this program on small-scale metallic structures are to understand plastic behavior related to cyclic loading and to identify mechanisms that determine fatigue lifetimes for low-and high-cycle regimes. Both cyclic plasticity and fatigue are evaluated in terms of sample state, particularly thickness and microstructure. The effects of testing conditions, including strain rate, ambient atmosphere and temperature, are evaluated. Emphasis is placed on identifying the key parameters that differentiate the behavior of freestanding metal thin films from that of bulk metals and that of thin metal films adhered to substrates. Unique apparatus under development fits into the specimen chamber of an Environmental Scanning Electron Microscope equipped with an Orientation Imaging Microscopy unit. This arrangement allows in-situ monitoring of surface morphology and microstructure during testing. Uniaxial tensile samples are used for simplicity of testing and analysis. Metal specimens are patterned at the Stanford Nanofabrication Facility using fabrication techniques developed in a preliminary study. Materials systems include aluminum (a FCC low melting point metal), iridium (a high melting point FCC metal), and molybdenum (a high melting point BCC metal). Improved understanding of thin film mechanical behavior will be transmitted to students through three paths: training of graduate and undergraduate research assistants, development of a specialized graduate mechanical behavior course, and integration of thin film mechanical behavior into the undergraduate curriculum.%%%Physics-based mechanical behavior models will allow dynamic modeling of device behavior and reliability for performance optimization. Technologies that will benefit include MEMS products such as high frequency RF switches and resonators for precision electronics. Relevant mesoscale applications include devices such as miniature aircraft and gas turbines for power generation. The target audience for this work includes university researchers, developers of design software, small-scale device manufacturers, and endusers of this technology.***