The Woodruff School

SUMMARY

The main objective of this thesis is to develop a comprehensive understanding of the various deformation
mechanisms pertaining to strain hardening, especially in the case of low-symmetry materials, such as hexagonal
close-packed Magnesium. To this end, modelling approaches are developed at two length scales: 1) At the
macroscale, a constitutive framework capable of receiving information from lower scales, the Hybrid strain
hardening Model, is developed and highlights the crucial role of latent interactions between deformation
modes and systems, and 2) At fine scale, a discrete dislocation dynamics (DDD) tool which allows for the
incorporation of anisotropic elasticity and elastic inhomogeneities is developed to study the collective effect
of dislocation-dislocation interactions, quantify their strength and their effect on latent-hardening, especially
in the case of pure Mg. In addition, the effects of dislocation-twin interaction and precipitate hardening are
addressed. It is expected that new constitutive laws suitable for complex loadings could be further developed
such as to directly account for local mechanisms and effects extracted from this work, thereby achieving the
scale transition between mesoscale and macroscale.

SUBJECT:	Ph.D. Proposal Presentation

BY:	Nicolas Bertin

TIME:	Monday, March 2, 2015, 10:00 a.m.

PLACE:	,

TITLE:	On the role of lattice defects interactions on strain hardening: a study from discrete dislocation dynamics to crystal plasticity modelling

COMMITTEE:	Dr. Laurent Capolungo, Chair (ME) Dr. David McDowell (ME) Dr. Surya Kilidindi (MSE) Dr. Hamid Garmestani (MSE) Dr. Carlos Tom� (Los Alamos National Laboratory)

SUMMARY The main objective of this thesis is to develop a comprehensive understanding of the various deformation mechanisms pertaining to strain hardening, especially in the case of low-symmetry materials, such as hexagonal close-packed Magnesium. To this end, modelling approaches are developed at two length scales: 1) At the macroscale, a constitutive framework capable of receiving information from lower scales, the Hybrid strain hardening Model, is developed and highlights the crucial role of latent interactions between deformation modes and systems, and 2) At fine scale, a discrete dislocation dynamics (DDD) tool which allows for the incorporation of anisotropic elasticity and elastic inhomogeneities is developed to study the collective effect of dislocation-dislocation interactions, quantify their strength and their effect on latent-hardening, especially in the case of pure Mg. In addition, the effects of dislocation-twin interaction and precipitate hardening are addressed. It is expected that new constitutive laws suitable for complex loadings could be further developed such as to directly account for local mechanisms and effects extracted from this work, thereby achieving the scale transition between mesoscale and macroscale.