Loading Metal Nanostructures Under Extreme Conditions Using Stress Waves with Rarefaction Shock Profiles

本研究项目结合实验和多尺度建模努力，研究在极高的应力和应变速率下金属中发生的新型变形机制。在本研究中，纳米结构样品将受到激光产生的亚纳秒上升时间的应力波。因此，该材料在1纳秒内承受50千兆帕斯卡或更高的应力。这种材料对这种动态条件的响应在以前还没有被详细探讨过。激光冲击实验将结合同一样品变形前后的电镜表征和多尺度建模。这种方法使演化结构与压力和应变速率的实验参数直接相关。此外，样品几何形状易于建模，因此可以进行直接比较。这些研究将为实验观察和/或模拟预测新的变形机制奠定科学基础，并提供极端环境下材料稳定性的原子尺度理解。这项工作将有助于替代能源系统和先进装甲的设计。先进的纳米制造和显微镜，复杂的光学和机械测试，以及最先进的建模策略相结合，为研究生和本科生提供了优秀的跨学科培训。促进研究理念的认识：将为洛杉矶联合学区的高中生提供研究机会；研究成果将纳入工程课程；同时，将鼓励弱势群体和本科生参与研究活动。

This research project combines experimental and multi-scale modeling efforts to investigate novel deformation mechanisms occurring in metals during extremely high rates of stress and strain. In this study, nanostructured samples will be subjected to laser-generated stress waves of sub-nanosecond rise times. As a result, the material experiences 50 GigaPascals or higher stresses within 1 nanosecond. The material's response to such dynamic conditions has not been explored in detail before. The laser shock experiments will be combined with electron microscopic characterization of the same samples before and after deformation and multi-scale modeling. This approach enables direct correlation between the evolved structures and experimental parameters of pressure and strain rate. Additionally, the sample geometries are amenable to modeling and thereby allowing for a direct comparison. These studies will establish scientific underpinning for the experimentally-observed and/or simulation-predicted new deformation mechanisms and provide an atomic-scale understanding of the material stability in extreme environments. The work should help in the design of alternate energy systems and advanced armors. The combination of advanced nanofabrication and microscopy, sophisticated optics and mechanical testing, and state-of-the-art modeling strategies provides excellent interdisciplinary training for graduate students and undergraduates. To promote awareness of the research ideas: the Los Angeles Unified School District high-school students will be provided with research opportunities; research results will be integrated into the engineering curriculum; and, underrepresented groups and undergraduates will be encouraged to participate in the research activities.