SUBJECT: Ph.D. Dissertation Defense
BY: Zhi Zeng
TIME: Thursday, February 2, 2017, 12:00 p.m.
PLACE: MRDC Building, 4211
TITLE: Multiscale Modeling and Uncertainty Analysis of Mechanical Behaviors of Nanostructured Metals
COMMITTEE: Dr. Ting Zhu, Chair (ME)
Dr. David L. McDowell (ME)
Dr. Chaitanya Deo (ME)
Dr. Christopher Saldana (ME)
Dr. Hamid Garmestani (MSE)


Nanostructured metals with heterogeneous structures achieve a synergy of ultra-high strength and ductility. These materials are called heterogeneous nanostructured metals. To provide a fundamental understanding of the mechanics and physical mechanisms governing the strength and ductility in heterogeneous nanostructured metals, we conduct both atomistic and crystal plasticity modeling studies of heterogeneous nanostructured metals in this thesis. The heterogeneous nanostructured metals studied in this thesis are gradient nano-grained copper, transmodal aluminum and additively manufactured stainless steel. A unifying modeling approach is applied. Specifically, we develop Voronoi tessellation-based geometrical models to build the nano-grained structures. The distribution of grain size and the spatial arrangement of nonuniform grains are fully controllable. We develop a crystal plasticity finite element model that accounts for grain-size-dependent yield strengths. The associated finite element simulations reveal both the gradient stress and gradient plastic strain. The molecular dynamics simulations reveal grain boundary-dominated plastic deformation. Moreover, we also study the unit processes of plastic deformation, including dislocation slip, deformation twinning and grain boundary sliding. These plastic deformation processes are competing with each other under the high stress field in the deformation of nanostructured metals. The uncertainties arising from heterogeneous nano-grained structures are studied and quantified. This thesis work provides the fundamental understanding of strength and ductility as well as unit deformation mechanisms of nanostructured metals. Furthermore, our uncertainty study has important implications for the design and fabrication of nanostructured materials.