Investigating the Shear Localization Mechanisms in Bulk Metallic Glasses via Novel Energy Landscape Exploration Techniques

该基金的研究目标是开发新的原子建模方法来探索势能景观，以阐明在实验相关的时间尺度上大块金属玻璃（BMG）中的基本原子剪切变形和局部化机制。 由于它们的弹性模量与许多金属相同，BMG提供了在室温下表现出高强度和中等韧性的材料的诱人可能性，在燃料电池，航空航天，汽车零件，体育用品和医疗器械中具有一系列潜在的应用。 BMG的一个关键的未解决的问题是，控制剪切转变区（STZ），这是单位塑性变形机制的形成的原子细节，还没有被确定。 由于缺乏对BMG塑性的机械的、基于原子的理解，已经显著地抑制了BMG的进一步开发和应用。 研究目标的实现将有可能通过开发一种新的数值技术，称为自主盆地攀登（ABC）方法，它将产生一个自主的逃逸轨迹上的3 N维势能表面从任何亚稳态初始状态。 具体而言，PI将（1）开发ABC/动力学蒙特卡罗耦合算法，以研究实验相关应变率下的剪切局部化，（2）开发新的非局部不稳定性标准，以识别相互作用STZ的大小、形状和动力学，以及（3）开发统一的自学习方案，以大幅降低计算成本，当应用于BMG或任何其他原子系统时，可以访问与经典分子动力学相当的长度尺度（即几十纳米），同时还能够访问远远超出经典分子动力学的时间尺度。如果成功，这项研究将为理解导致局部剪切变形的基本非弹性变形机制做出原创性贡献，因此，特别是在BMG中，以及在一般的无定形固体中，会发生灾难性的失效。 此外，这些原子的变形机制和它们之间的关系，无定形固体的结构的知识将导致新的，原子通知连续变形和塑性理论的无定形固体。 教育和推广目标将侧重于（1）招募妇女和代表性不足的少数民族参与令人兴奋和迅速扩大的纳米材料研究领域，（2）向高中生推广，鼓励未来从事科学和工程职业，（3）通过跨学科建模工作开发的新课程材料和软件界面的新颖网络传播，教育和更广泛的影响，以及（4）在本科阶段的课程发展，以鼓励新生攻读科学和工程专业。

The research objective of this grant is to develop novel atomistic modeling approaches to explore the potential energy landscape in order to elucidate the fundamental atomistic shear deformation and localization mechanisms in bulk metallic glasses (BMGs) at experimentally relevant time scales. Because their elastic moduli are of the same order as many metals, BMGs offer the tantalizing possibility of a material that exhibits both high strength and moderate toughness at room temperature, with a range of potential applications in fuel cells, aerospace, auto parts, sporting goods, and medical devices. One key unresolved issue for BMGs is that the atomistic details governing the formation of shear transformation zones (STZ), which are the unit plastic deformation mechanism, have not been identified. This lack of a mechanistic, atomistically-based understanding of BMG plasticity has significantly inhibited the further development and application of BMGs. Accomplishment of the research objectives will be made possible by the development of a novel numerical technique, called the autonomous basin climbing (ABC) method, which will generate an autonomous escape trajectory on the 3N-dimensional potential energy surface from any metastable initial state. Specifically, the PI will (1) develop a coupled ABC/kinetic Monte Carlo algorithm that enables the study of shear localization at experimentally-relevant strain rates, (2) develop novel non-local instability criteria to identify the sizes, shapes, and dynamics of interacting STZs, and (3) develop a unified self-learning scheme to substantially reduce the computational cost such that the ABC method, when applied to BMGs or any other atomistic system, can access length scales that are comparable to classical molecular dynamics (i.e. tens of nanometers) while also being able to access time scales far beyond that of classical molecular dynamics.If successful, this research will make original contributions to understanding the fundamental inelastic deformation mechanisms that lead to localized shear deformation and thus catastrophic failure in BMGs specifically, and amorphous solids in general. Furthermore, knowledge of these atomistic deformation mechanisms and their relationship to the structure of amorphous solids will lead to new, atomistically-informed continuum deformation and plasticity theories for amorphous solids. Education and outreach objectives will focus on (1) recruitment of women and underrepresented minorities to participate in the exciting and rapidly expanding field of nanomaterials research, (2) outreach to high school students to encourage future careers in science and engineering, (3) novel web-based dissemination of both new course materials and software interfaces that are developed through this interdisciplinary modeling effort to link research, education, and broader impacts, and (4) course development at the undergraduate level to encourage freshmen to pursue majors in science and engineering.