Currently, the approach is twofold:

First:

3D Discrete Dislocation Dynamics mesoscopic simulations (using the parallelized code PARANOID developed by Dr. Schwarz, IBM Research) are carried out to better understand the effects of dislocation sources. In this approach, we consider a single crystal free standing films as a model of a columnar grain. The numerical results will be compared qualitatively with experimental measurements obtained in freestanding films and TEM observations of the tested specimens. The methodology will be extended to bi-crystals and multigrains in which grain boundaries and twin boundaries are obstacles to dislocation motion. For instance, Fig. 1 displays the evolution of dislocation loops models as Frank-Reed sources of various strengths randomly distributed within the grain.

Secondly:

A grain level FEM model based on Crystal Plasticity (UMAT-Abaqus) is used to take into account initial grain orientations and texture development during deformation through a representative volume element (RVE) of the tested samples. A new criterion describing the onset of plasticity for freestanding thin films is being incorporated in this continuum model based on the results of atomistic simulations and discrete dislocation dynamics simulations. The geometry of the RVE is based on polyhedrons obtained by Voronoi tessellations to represent more realistically the 3D extension of grain boundaries.

Our long term objective:

To couple simulation approaches in a "hierarchical" way.

Participating personnel:

• Horacio D. Espinosa (PI)
• Michele Panico (Graduate student)
• Stephane Berbenni (Post-Doc)
• Huang Tang (Post-Doc)
• Brian Hyde (Post-Doc)

Collaboror:

• Dr. Klaus W. Schwarz (IBM Research, Yorktown Heights, NY)
• Dr. Diana Farkas (Virginia Tech)
• Dr. Mike Baskes (Los Alamos National Lab)