3D DISCRETE DISLOCATION DYNAMICS APPLIED TO ... - NUMODIS

6 Introduction
computing has been investigated extensively and is now a well established field. From the success in
atomistic and continuum parallel simulations, we came to the conclusion that parallel computation
will be the best and the only choice in order to include a relatively high volume fraction of precip-
itates in the simulation volume, because a dramatic increase in computational power can only be
met through it.
A parallel DDD code thus has been developed and applied to the fatigue simulations containing a
large number of particles. The effects of particles on the fatigue properties are studied focusing on
the irreversibility of slips and the formation of the intense slip bands during the cyclic deformation.
The parallel DDD code developed would be of benefit to not only small scale simulations which
involve a large number of internal defects but also large scale simulations which would make a com-
parison with the macroscopic simulations possible. The parallel DDD code would hence reinforce
the role of the 3D DDD method in the series of the plasticity simulation methods.
This thesis is organized as follows.
Chapter 1 Introduction (this chapter)
Chapter 2 summarizes the theoretical backgrounds and methodologies of the 3D discrete disloca-
tion dynamics method. The computation of the displacement fields of a dislocation loop is
introduced. Several boundary conditions are explained, such as the implementation of internal
interfaces and the periodic boundary conditions. The numerical efficiency of the serial DDD
algorithm is increased by revisiting the so-called box method ([Verdier et al. 98]).
Chapter 3 presents the parallel algorithm developed to parallelize the 3D DDD program used
in this work. The parallel version of the DDD program aims at simulating fatigue tests of
materials containing large number of particles in reasonable time using parallel computers.
The new parallel DDD program is tested and improved in performance by balancing the load
dynamically, and then applied to stage I-II simulations. This chapter also contains general
introduction to parallel computing.
Chapter 4 contains three applications of the method developed and detailed in the preceding
chapters. Image stresses by a cylindrical, spherical and cubical particle are computed. The
effects of image stresses on flow stresses and hardening are investigated. The FEM/DDD