Size Effects, Deformation, Strength and Fracture of Nanotwinned Metals

本项目的目的是研究最近合成的具有高密度纳米孪晶片的超细晶金属的力学性能和变形机制。为了揭示这类材料的变形行为如何依赖于内部微观结构和相关的特征长度尺度（即晶粒尺寸和孪晶界间距），我们将应用多尺度建模方法，结合有限元（连续体和介观），位错动力学（介观和微观）和分子动力学（原子尺度）方法。超大尺度的数值模拟和理论建模将用于捕获这种纳米孪晶金属中的各种变形机制，包括位错、裂纹和孪晶边界之间的相互作用。纳米孪晶金属是一种新型的分层纳米结构材料，具有超高强度、惊人的延展性、增强的应变硬化、高应变率敏感性、卓越的断裂韧性和抗疲劳性的不同寻常的组合。材料研究中大规模计算能力的进步将使美国在科学和技术上保持世界领先地位。该项目的教育组成部分包括培养一名博士生，指导本科生，并将最先进的研究成果融入布朗大学现有的研究生和本科工程课程中，目前学生对分层纳米结构材料和结构的力学有浓厚的兴趣。额外的外展活动将由布朗调解？材料研究科学与工程中心（MRSEC）建立了一套优秀的外联教育项目。

The goal of this project is to investigate the mechanical properties and deformation mechanisms of recently synthesized ultrafine-grained metals with a high density of nanoscale twin lamellae that act as subgrain microstructures. To reveal how the deformation behaviors of this kind of materials depends on the internal microstructures and associated characteristic length scales (i.e., grain size and twin boundary spacing), we will apply a multiscale modeling approach that combines finite element (continuum and mesoscopic), dislocation dynamics (mesoscopic and microscopic) and molecular dynamics (atomic scale) methods. Ultra-large scale numerical simulations and theoretical modeling will be performed to capture various deformation mechanisms in such nanotwinned metals, including the interaction between dislocations, cracks and twin boundaries.The proposed research will generate new knowledge and fundamental understanding of nanotwinned metals, a new class of hierarchical nanostructured materials that possess an unusual combination of ultra-high strength, amazing ductility, enhanced strain hardening, high strain-rate sensitivity, remarkable fracture toughness and fatigue resistance. The advance of large-scale computational capabilities in materials research will enable USA to maintain scientific and technical leadership in the world. The educational components of the project include training of a PhD student, mentoring of undergraduates, and assimilation of state-of-the-art research results into the existing graduate and undergraduate courses in engineering at Brown University where there are currently strong student interests in mechanics of hierarchically nanostructured materials and structures. Additional outreach activities will be mediated by Brown?s Materials Research Science and Engineering Center (MRSEC) which has established a set of excellent outreach educational programs.