Homogeneous Dislocation Nucleation

这项工作将利用介观尺度分析技术来研究压痕驱动的完整晶体中的位错成核。特别是，中尺度区域的线性机械响应，中间的原子尺度和完整的系统大小，将被探测，以寻找胚胎缺陷。 原子计算机模拟将使用经典的经验势来研究在光滑的纳米级压头下的完美薄膜中的过程。 此外，形核现象将在一个连续的框架，场位错力学（FDM）的研究。 直接比较将与原位电子显微镜成像过程中压痕的单晶Al。最终的目标是构建一个简单的分析框架，这将能够预测热激活障碍的控制核给定几个简单的材料参数和几何加载条件作为inputs.The当前国家的最先进的预测塑性变形韧性金属仍然主要是经验和唯象。 一个“第一原理”，自下而上，塑性的定量理解将允许设计具有最佳机械性能的材料，如增加强度和韧性。 这项工作还将涉及通过匹兹堡超级计算中心协调的中等教育外展，目标是匹兹堡市中心代表性不足的人口。

This work will utilize meso-scale analysis techniques to study indentation driven nucleation of dislocations in perfect crystals. In particular, the linear mechanical response of mesoscale regions, intermediate between the atomic scale and full system size, will be probed in order to search for embryonic defects. Atomistic computer simulations will be performed using classical empirical potentials to study the process in a perfect thin-film under a smooth, nanometer-scale, indenter. Furthermore, the nucleation phenomenon will be studied within a continuum framework, field dislocation mechanics (FDM). Direct comparisons will be made with in-situ electron microscopy imaging during indentation of single-crystal Al. The ultimate goal is to construct a simple analytical framework which would be able to predict thermal activation barriers governing nucleation given a few simple material parameters and geometrical loading conditions as inputs.The current state-of-the-art for predicting plastic deformation in ductile metals remains largely empirical and phenomenological. A "first principles," bottom-up, quantitative understanding of plasticity would allow for the design of materials with optimal mechanical properties such as increased strength and toughness. The work will also involve secondary education outreach co-ordinated through the Pittsburgh Supercomputing Center and targeted at under-represented populations in the urban core of Pittsburgh.