Dislocations Jam at any Density

1. Dislocations Jam at any DensityPlasticity and Avalanches: Connections Between Systems Ranging from Metals to Granular MaterialsKarin A. Dahmen, University of Illinois, Urbana Champaign, DMR 1005209 • Dislocations Jam at any Density • Motivation: In our recent Physical Review Lettersarticle (with graduate student Georgios Tsekenis and Nigel Goldenfeld), we show that dislocations jam at any density (in contrast to granular materials which do not jam at densities lower than a critical density). This study links the field of plasticity in crystals with recent studies of the jamming transition in granular materials. • Methods: We use an analytical scaling analysis and dislocation dynamics simulations. • Results: • a general argument why dislocations jam at any density that can be generalized to other systems with long range interactions. • Simulation results for the flow stress as a function of system size and dislocation density, that agree with the analytical predictions. • We propose a jamming phase diagram for dislocation systems. • Proposed phase diagram for dislocation systems. Notice the absence of a jamming point. • For details, see Georgios Tskenis, Nigel Goldenfeld, and Karin A. Dahmen, Phys. Rev. Lett. 106, 105501 (2011).

2. Dislocations Jam at any Density: Broader ImpactsPlasticity and Avalanches: Connections Between Systems Ranging from Metals to Granular MaterialsKarin A. Dahmen, University of Illinois, Urbana Champaign, DMR 1005209 • The studies on dislocation dynamics are relevant to materials testing, material failure prediction, and the study of materials properties on a wide range of scales (predictions are relevant for experiments down to the nanometer scale, see figure to the right). • 2 graduate students and 1 undergraduate student are trained in modern research methods from physics, materials science and engineering, through the interdisciplinary projects and collaborations with experimentalists, theorists, and engineers. Relevance of theory to nanopillar compression experiments done by J. Greer (Caltech). Shown are an Au nanopillar (a)(c ) and Mo nanopillar (b)(d) before and after compression. (courtesy Julia .Greer, Caltech) • Organization of the • international 2011 Illinois • workshop on Fluctuations and • Collective Phenomena in • Disordered Materials (co- • funded by the Materials • Computation Center (NSF) and • the Institute for Condensed • Matter Theory at Illinois).