Size Effects, Deformation, Strength and Fracture of Nanotwinned Metals

该项目的目标是研究最近合成的超细晶粒金属的机械性能和变形机制，该金属具有高密度的纳米级孪晶层，作为亚晶粒微观结构。为了揭示这类材料的变形行为如何取决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（连续和介观），位错动力学（介观和微观）和分子动力学（原子尺度）的方法。超大规模的数值模拟和理论模型将被用来捕捉这种纳米孪晶金属中的各种变形机制，包括位错、裂纹和孪晶界之间的相互作用。拟议的研究将产生对纳米孪晶金属的新知识和基本理解，纳米孪晶金属是一类新的分级纳米结构材料，具有超高强度、惊人的延展性、强化的应变硬化、高应变率敏感性、显著的断裂韧性和抗疲劳性。材料研究中大规模计算能力的进步将使美国在世界上保持科学和技术领先地位。该项目的教育组成部分包括博士生的培训，本科生的指导，并同化国家的最先进的研究成果到现有的研究生和本科生课程的工程在布朗大学，目前有强烈的学生兴趣在力学的层次纳米结构材料和结构。额外的外联活动将由布朗调解？材料研究科学与工程中心（MRSEC）建立了一套优秀的外展教育计划。

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.