Size Effects, Deformation, Strength and Fracture of Nanotwinned Metals

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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.