On the Mechanics of Ripplocations: A New Defect in Layered Solids

层状材料的最新发现为定制更好的材料开辟了新的维度。层状材料在我们周围的环境中无处不在；它们包括石墨、云母和二维固体(具有原子尺度的厚度)，以及许多其他物质。长期以来，人们一直认为，要使固体变形，必须存在微观缺陷。直到最近，这些缺陷还被推定为称为位错的线缺陷，这是一种众所周知的、经过研究的材料缺陷。然而，2016年的研究表明，关于层状材料的变形，传统观点是不正确的，或者是不完整的。一种潜在的新的微观机制被称为涟漪，最好的描述是原子尺度的涟漪，被认为是控制机制。在宏观尺度上，涟漪将是地毯涟漪。目前，人们对这些缺陷、它们的机理或行为，以及如何利用它们来创造改进的材料知之甚少。这项研究通过在两个长度尺度上的一套集成的建模和实验来研究涟漪定位的机理。总体目标是整合力学、材料科学和科学计算领域，建立一个设计更先进材料的平台，并为与层状材料相关的技术部门提供基础知识基础，如地球技术和微电子。此外，作为研究的一部分，将通过暑期项目接触高中生，聘请来自代表性不足群体的本科生和研究生进行研究，并将互动学习模块添加到课程中，以培养下一代不同的科学家和工程师。涟漪行为和错位行为之间存在基本差异，并激励着当前的项目。根据位错理论，当层状固体材料的平面在边缘加载和卸载时，如果是弹性材料，它们要么可逆变形，并恢复到原始形状而不耗散任何能量，要么保持永久凹陷。Ripplocation行为解释了观察到的第三种选择，即材料恢复到原来的形式，同时消耗相当大的能量。这项工作的目标是在多个层面上了解涟漪机制，从原子，通过分子建模和理论，到宏观的层状固体将被压入。分子模拟的结果，以捕捉涟漪的基本物理，将被用来创建一个新的涟漪动力学模型。模型中的压痕预测，包括强度和微结构变形，将直接与纳米尺度的原子模拟和微尺度的实验压痕研究的结果进行比较和验证。其目的是证明涟漪定位机制是尺度不变的，并提供一个基于力学的预测框架，该框架可以扩展到无数其他层状材料，以实现改进的设计策略。

Recent discoveries in layered materials have opened new dimensions for tailoring better materials. Layered materials are ubiquitous in our surroundings; they encompass graphite, mica, and two-dimensional solids (with an atomic-scale thickness), among many others. It has long been understood that for solids to deform, microscopic defects must be present. Up to quite recently these defects were presumed to be line defects called dislocations, a well-known and studied material defect. In 2016, however, research suggested that conventional wisdom was incorrect, or incomplete, regarding the deformation of layered materials. A potentially new micro-mechanism called a ripplocation, best described as an atomic scale ripple, was suggested as the governing mechanism. At the macroscale, a ripplocation would be a carpet ripple. Currently, little is known about these defects, their mechanics or behavior, and how to leverage them to create improved materials. This research investigates the mechanics of ripplocation through an integrated suite of modeling and experimentation at two length scales. The overall goal integrates fields of mechanics, materials science, and scientific computing to build a platform to engineer more advanced materials as well as provide fundamental knowledgebase to the technology sectors where layers materials are relevant, such as geo-technology and microelectronics. Also, as part of the research, outreach to high school students will be made through summer programs, undergraduate and graduate students from underrepresented groups will be hired to perform research, and interactive learning modules will be added to the curriculum to educate the next generation of diverse scientists and engineers.Fundamental differences between ripplocation and dislocation behavior exist and motivate the current project. According to dislocation theory, when the planes of layered solid materials are loaded and unloaded edge-on they will either reversibly deform, and return to their original form without dissipating any energy if it's an elastic material or they will remain permanently indented. Ripplocation behavior explains the third observed option, which is the material returning to its original form, while dissipating considerable amounts of energy. The goal of this work is to understand ripplocation mechanics at multiple levels, from the atomic, through molecular modeling and theory, to the macroscopic where layered solids will be indented. Results from molecular modeling to capture the fundamental physics of ripplocations will be leveraged to create a new ripplocation dynamics model. Indentation predictions, including both strength and microstructural deformation, from the model will be directly compared to and verified with results from atomistic modeling at the nanoscale and experimental indentation studies at the microscale. The goal is to show that ripplocation mechanics are scale invariant and provide a mechanics-based predictive framework that can be extended to a myriad of other layered materials to enable improved design strategies.