Continuum and atomistic aspects of dislocation dynamics
- Dislocation dynamics (DD) simulations have been developed to link the plastic deformation of single crystals with the microscopic dynamics of dislocations. Most of the existing DD simulation programs are limited to isotropic elasticity, even though most single crystals are elastically anisotropic. Understanding the connection between DD and plasticity under these conditions requires an efficient DD simulation program that can account for anisotropic elasticity. Cross-slip is also an aspect of dislocation dynamics, which plays an important role in the plastic deformation of FCC metals, leading to hardening and dynamic recovery. However, a satisfactory cross-slip model has not yet been implemented in DD simulations, which accurately reflects the dependence of energy barrier on the local stress. To enable efficient computation of forces on dislocation segments in an anisotropic linear elastic medium, several alternative approaches are investigated and explicit expressions are derived for self-stress and self-force. These can be used to compute short range stress fields in DD simulations. To compute long-range interactions between distant dislocation segments, the fast multipole method (FMM) proves to be efficient; however, FMM has not yet been applied to three dimensional DD simulations which take into account anisotropic elasticity. A systematic procedure is demonstrated to establish this capability by first obtaining the derivatives of the elastic Green's function to arbitrary order for a medium of general anisotropy. Then the stress fields of dislocation segments are computed using multipole expansions based on these derivatives. These algorithm advances enable efficient calculations of both short range and long range stress fields in DD simulations. Both continuum and atomistic study of dislocation cross-slip is performed. To construct a cross-slip rate function of the local stress state, the line tension model following Stroh and Escaig is studied and the cross-slip energy barriers are computed numerically. To provide an atomistic understanding of cross-slip mechanism, molecular dynamics (MD) simulations are performed to investigate the phenomenon under different stress conditions. Cross-slip energy barriers are evaluated and are compared with numerical results given by the line tension model. These studies lead to cross slip rate predictions as a function of local stress, which are suitable for use in DD simulations.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Stanford University, Department of Materials Science and Engineering.
|Nix, William D
|Nix, William D
|Statement of responsibility
|Submitted to the Department of Materials Science and Engineering.
|Thesis (Ph.D.)--Stanford University, 2013.
- © 2013 by Jie Yin
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