ROLE OF THE SECONDARY SLIP SYSTEM IN A COMPUTER-SIMULATION MODEL OF THE PLASTIC BEHAVIOR OF SINGLE-CRYSTALS

A computer simulation model is proposed for investigating the plastic behaviour of single crystals oriented for single slip. To match transmission electron microscopy results our model consists of a dislocation system of parallel straight edge dislocations with a maximum of two different Burgers vectors, yielding essentially a two-dimensional problem. The velocity of the dislocations is taken to be proportional to the local shear stress, and generation of new dislocations is allowed. On the basis of the continuum theory of dislocations a special equation is set up to simulate a tensile deformation experiment with constant rate. An AMT DAP computer was used for the computations. In the first simulations, dislocation motion was allowed only in one slip system. This relatively simple case is enough to reproduce the properties of stage I of the deformation of single crystals. During the deformation the dislocations tend to arrange in sheets parallel to the slip direction. There is no sign of cell formation, but a long-range fluctuation appears in the stress field of the dislocations. In a couple of simulations we introduce two slip systems with 45-degrees and 105-degrees angles to the tensile axis, whereupon after stage I the stress starts to increase much more rapidly as the dislocations start to form walls and cells.