3.032 Mechanical Behavior of MaterialsFall 2007Using U(r): Measure parameters for U(r) in physical model to predict stresses that are high enough forelastic instabilities to occur (e.g., nucleation of defects in crystals).Lecture 13 (10.10.07)How does stress to move atoms depend on size of grains in polycrystalline metals?σiior τij~ dU/drRaft of soap bubbles with interbubble potential similar to interatomic potential of fccmetals, under distributed force of an indenter.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): 656andFig. 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. Van Vliet et al., Nature (2002); Phys Rev B (2003); Phil Mag A (2003)3.032 Mechanical Behavior of MaterialsFall 2007Using 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.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)Courtesy of Sidney Yip. Used with permission.Electrospun PEO could be used for filters, composites, fuel cells, drug delivery, cell scaffolds, etc. [Rutledge Group, MIT]3.032 Mechanical Behavior of MaterialsFall 2007Using U(r):Polymer nanofibers: Do physical and mechanical properties differ from bulk polymers?Internal energy inside polymer nanofiber increases for fibers of R < 5 nm.Curgul, Rutledge and Van Vliet, Macromolecules (2007, in press)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.Courtesy Gregory Rutledge. Used with permission.Curgul, Rutledge and Van Vliet, Macromolecules (2007, in press) 3.032 Mechanical Behavior of MaterialsFall 2007Using U(r):Polymer nanofibers exhibit lower glass transition temperature and elastic deformation up to 5% normal strain.Lecture 13 (10.10.07Image 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): 8483-8489.0102030405060700 0.05 0.1 0.15 0.2 0.25 0.3 0.35Strain along zσzz[MPa]εzzE ~ 750
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