Homogeneous Dislocation Nucleation

这项工作将利用中尺度分析技术来研究完美晶体中由压痕驱动的位错成核。特别是，中尺度区域的线性力学响应，介于原子尺度和全系统尺寸之间，将被探索，以寻找胚胎缺陷。原子计算机模拟将使用经典经验势来研究在光滑的纳米压头下完美薄膜中的过程。此外，成核现象将在连续介质框架，场位错力学（FDM）中进行研究。将与单晶Al压痕过程中的原位电子显微镜成像进行直接比较。最终目标是构建一个简单的分析框架，该框架能够在给定几个简单的材料参数和几何加载条件作为输入的情况下预测控制成核的热激活势垒。目前预测韧性金属塑性变形的最新技术仍然主要是经验和现象学的。“第一性原理”，自下而上，对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，目标是匹兹堡城市核心地区代表性不足的人口。

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.