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 transm ission electron microscopy results our model consists of a dislocation system of parallel straight edge dislocations with a maximum of two d ifferent Burgers vectors, yielding essentially a two-dimensional probl em. The velocity of the dislocations is taken to be proportional to th e local shear stress, and generation of new dislocations is allowed. O n 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. T his relatively simple case is enough to reproduce the properties of st age I of the deformation of single crystals. During the deformation th e dislocations tend to arrange in sheets parallel to the slip directio n. There is no sign of cell formation, but a long-range fluctuation ap pears in the stress field of the dislocations. In a couple of simulati ons we introduce two slip systems with 45-degrees and 105-degrees angl es to the tensile axis, whereupon after stage I the stress starts to i ncrease much more rapidly as the dislocations start to form walls and cells.