3 032 Mechanical Behavior of Materials Fall 2007 Using U r Measure parameters for U r in physical model to predict stresses that are high enough for elastic instabilities to occur e g nucleation of defects in crystals Images removed due to copyright restrictions Please see Fig 1c in Gouldstone Andrew et al Simulation of Defect Nucleation in a Crystal Nature 411 July 2001 656 and Fig 1 in Van Vliet Krystyn J et al Model Experiments for Direct Visualization of Grain Boundary Deformation in Nanocrystalline Metals Applied Physics Letters 83 August 2003 1441 1443 Raft of soap bubbles with interbubble potential similar to interatomic potential of fcc metals under distributed force of an indenter Van Vliet et al Nature 2002 Phys Rev B 2003 Phil Mag A 2003 How does stress to move atoms depend on size of grains in polycrystalline metals ii or ij dU dr Lecture 13 10 10 07 3 032 Mechanical Behavior of Materials Fall 2007 Using U r Molecular dynamics simulations move atoms according to Newton s Law F ma where F dU dr and U interatomic potential such as L J potential Courtesy of Sidney Yip Used with permission Thin film of aluminum moving atoms according to U r under distributed load of spherical indenter Atom color atomic coordination number Li Van Vliet et al Nature 2003 Phys Rev B 2004 Lecture 13 10 10 07 3 032 Mechanical Behavior of Materials Fall 2007 Using U r Polymer nanofibers Do physical and mechanical properties differ from bulk polymers Courtesy Gregory Rutledge Used with permission Images removed due to copyright restrictions Please see Fig 1 and 4 in Curgul Sezen et al Molecular Dynamics Simulation of Size Dependent Structural and Thermal Properties of Polymer Nanofibers Macromolecules 40 2007 8483 8489 Electrospun PEO could be used for filters composites fuel cells drug delivery cell scaffolds etc Rutledge Group MIT Internal energy inside polymer nanofiber increases for fibers of R 5 nm Curgul Rutledge and Van Vliet Macromolecules 2007 in press 3 032 Mechanical Behavior of Materials Fall 2007 Image removed due to copyright restrictions Please see Fig 7 and 10 and Eqn 1 in Curgul Sezen et al Molecular Dynamics Simulation of Size Dependent Structural and Thermal Properties of Polymer Nanofibers Macromolecules 40 2007 8483 8489 zz MPa Using U r Polymer nanofibers exhibit lower glass transition temperature and elastic deformation up to 5 normal strain 70 60 50 40 30 20 10 0 E 750 MPa 0 0 05 0 1 0 15 0 2 0 25 0 3 0 35 zzalong z Strain Curgul Rutledge and Van Vliet Macromolecules 2007 in press Lecture 13 10 10 07