Title: The 3-D Dislocation Dynamics Method: Applications and Capabilities

Speaker: Tariq A. Khraishi, University of New Mexico

Date/Time: Wednesday, October 3, 2007, 10:00 am - 11:00 am

Location: CSRI Building, Room 90 (Sandia NM)

Brief Abstract: In recent years, 3-D discrete dislocation dynamics (DD) has gained much attention in studies of crystal plasticity. DD is a numerical model (fortified with theory) that can capture the motion and short- and long-range interaction of dislocation lines, each lying on a physical glide plane with permissible Burgers vector (of magnitude b). The simulation cell is typically a 5-30 mm box subjected to constant stress or constant strain-rate. Here, each dislocation is approximated by a set of linear segments (typically 100b-500b). The elastic interaction of these segments is accounted for using explicit expressions for their self-stress fields (an O(N2) operation). The segments also feel the effect of externally applied loads. The calculation of the Peach-Koehler force acting on a segment then follows from these elastic effects. Motion of a dislocation segment is a function of the glide force and the dislocation mobility. Here, effects like temperature and lattice friction (i.e. Peierls stress) can be taken into account. Also, events like dislocation cross-slip, annihilation, jog formation, etc., introduce themselves seamlessly into the computation. The solution is incrementally marched in time and terminated at will.
 
DD can thus capture the evolving structure of an ensemble of dislocations (of real densities) in a fundamental manner. It offers the promise of linking the different scales (nano to macro scales). A few of the applications of DD are exhibited including the study of irradiated materials and nano-indentation experiments. For example, DD can capture irradiation-induced hardening and, upon stress, the formation of defect-free channels in irradiated single crystals. Finally, other developments in DD will be exhibited. This includes the treatment of external traction-free surfaces using the distributed dislocation method. This has relevance in thin films as well as surface steps and associated stress risers. Other developments regard the interaction of dislocations with internal rigid particles and grain boundaries. These are important strengthening mechanisms in metals. Other future possibilities will also be discussed.