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

namics codes into a parallel version, especially in Lawrence Livermore National Laboratory (LLNL)
and University of California in Los Angeles (UCLA). Both of them use the nodal model.
The image stresses due to a 3D particle were computed using the FEM/DDD coupling code. The
interaction of a dislocation line with a circular cylindrical, spherical and cubical particle with differ-
ing elastic modulus was investigated. The computation method was validated by comparing with
the corresponding analytical solutions. It was shown that the image stresses need to be taken into
account especially in the study of the local events around the particles, e.g. the computation of the
energy state around a particle and the calculation of the creep threshold stresses at high tempera-
tures.
In these modeling, it is necessary to mesh the whole simulation volume because the geometrical
symmetries are broken by the heterogeneous force boundary conditions due to a dislocation. Conse-
quently, the cost of the FEM computation is relatively high both in term of cpu time and required
memory. The force profiles fitted from the computed data can used as approximation solutions of
interactions due to the elastic modulus mismatch. For the dynamics, however, the use of a parallel
finite element method would be of benefit and will be served as a good tool in studying the plasticity
of multilayer films, for example.
The effect of the elastic modulus mismatch is investigated focusing on the flow stress and the
subsequent hardening behavior using the simple geometry involving two particles. The characteris-
tics of the image stresses (short-ranged and paraelastic) generate minor effects on the yield stresses
but significant effects on the work hardening rate. The image stresses are also found to affect sig-
nificantly the local events such as cross slip and climb.
The fatigue simulations are performed using the internal interfaces represented by facets and the
new parallel DDD program. The characters of shearable and non-shearable particles and the par-
ticle’s strength evolution by shearing-off were represented in a simplified manner by adjusting the
strength of the facets.
Major features of the fatigue properties of materials hardened by shearable and non-shearable par-
ticles are well reproduced by the simulations, e.g. microstructure of the intense slip bands, the
cyclic mechanical response and the surface markings. The simulated results were compared with
the available experimental observations, and showed good agreements in a qualitative way. The
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