**CANCELLED - to be rescheduled** Prof. Benoit Devincre (LEM, CNRS/ONERA, France)

Improving crystal plasticity models with dislocation dynamics simulations
When Nov 21, 2016
from 02:00 PM to 03:00 PM
Where LR8
Contact Name
Contact Phone 01865-283446
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Plastic deformation of crystalline materials is mainly the result of the collective movement of dislocations, in the response of their mutual interactions, external applied loading and interactions with boundaries such as free surfaces, interfaces or grain boundaries. The dislocation microstructures emerging from such dynamics are intrinsically heterogeneous and the way they affect the mechanical properties is a puzzling problem. Therefore, the development of constitutive equations for the modeling of this multiscale problem is a challenging issue confronting materials science. After two decades of developments, three dimensional Dislocation Dynamics (3D-DD) simulation comes out as a remarkable tool to investigate such problem. In this presentation, investigation of strain hardening in FCC crystals is presented and discussed from the viewpoint of scale transitions. This analysis is based on the storage recovery framework expanded at the scale of slip systems. Use of 3D-DD simulations is systematically made to guide and justify an improved formulation of a crystal plasticity model and to calculate the latter parameter values. Attention is focused on the forest interactions believed to control isotropic hardening and the internal stress (backstress) associated with dislocation patterning that is believed to control kinematic hardening. Among the different elementary features controlling both strain hardening phenomena, we show that junction strength and mobile dislocation mean free path are key physical parameters to understand the dislocation microstructure asymmetry upon load path changes. A model accounting for the dislocation short-range properties observed in DD simulation is proposed. This model captures quantitatively many details of the existing experiments on monotonic tensile tests, Baushinger tests and cyclic tests made on FCC single crystals.