1. CAREER: Microstructure & Size Effects on Metal Plasticity at Limited Length Scale Frederic Sansoz, University of Vermont, DMR 0747658 Animated snapshots of molecular dynamics (MD) simulations showing the diameter dependence of plastic elongation in twinned gold nanowires under constant tensile stress (  =3.65 GPa). The colored layers represent different twinned grains. Objectives. The two foci of the research activities are: 1.To use atomistic simulation to characterize the complex interactions between lattice dislocations, free surfaces and twin boundaries in gold and nickel nanowires under deformation 2.To experimentally measure size effects on strength and strain-hardening in gold and nickel nanowires using applied electrochemical methods and atomic force microscopy The ultimate goal: To create new metallic nanomaterials with defects that can make them stronger A summary of significant results include: 1.MD simulation of size effects on the yielding and plastic flow of gold nanowires containing nanoscale growth twin boundaries. 2.MD simulation of softening effects in small single-crystal Ni nanowires deformed by nanoindentation. 3.Theoretical study of mechanistic interactions between lattice dislocation and coherent twin boundary. 4.Structure and mechanical properties of single-crystal Ni nanowires synthesized by electrodeposition and deformed by atomic force microscopy-enabled nanoindentation.

2. This project also has made broader impacts through… …Education Training and education of graduate and undergraduate students in the fields of mechanical engineering and materials science are fully integrated to the research project. To date, one Ph.D. student (Virginie Dupont) has successfully completed her thesis, one more (Chuang Deng) is in progress, both in the atomistic simulation of nanowires, and one B.S. student (Zachary Burchman) has completed his Honors thesis on the synthesis of electrodeposited Ni nanowires. …Dissemination of knowledge Our work is also to disseminate the new knowledge gained from our research through the publication of scholarly articles, and the presentation at international conferences. Recent publications in this area include: 1.F. Sansoz, H. Huang and D.H. Warner, “An Atomistic Perspective on Twinning Phenomena in Nano-enhanced FCC Metals”, JOM, 9, 79-84 (2008) 2.F. Sansoz and C. Deng, “Comment on “Deformation mechanisms of face-centered-cubic metal nanowires with twin boundaries” Appl. Phys. Lett. 90, 151909 (2007)”, Applied Physics Letters, 93, 086101 (2008). 3.V. Dupont and F. Sansoz, "Quasicontinuum Study of Incipient Plasticity under Nanoscale Contact in Nanocrystalline Aluminum", Acta Materialia, in press (2008) 4.V. Dupont and F. Sansoz, “Molecular Dynamics Study of Crystal Plasticity during Nanoindentation in Ni Nanowires”, Journal of Materials Research – Focus Issue on Indentation Methods in Advanced Materials Research, in review. CAREER: Microstructure & Size Effects on Metal Plasticity at Limited Length Scale Frederic Sansoz, University of Vermont, DMR 0747658 Virginie Dupont Chuang Deng Zack Burchman