Investigation of Alkali metal embrittlement of Aluminum Lithium alloys using first principles calculations and dislocation theory

Segregation of alkaline earth metals at grain boundaries is investigated as a cause of grain boundary embrittlement in Aluminum alloys. Auger spectroscopy shows that grain boundary segregation of Na occurs in an Al­Li alloys. In addition, Aluminum extracted from bauxite bring in alkali impurities. First-principles simulation allows us to understand the energetics of Na segregation at grain boundaries and model the decreased grain boundary cohesive energy. Using this data within the concomitant dislocation theory based on our recent work, we study the effect of Na segregation on static and fatigue fracture of Al-Li alloys. Using DFT calculations, we describe how the presence of alkali impurities could possibly enhance hydrogen embrittlement

Uncertainty Quantification of Microstructural Properties due to Experimental Variations

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143074/1/1.J055689.pd

Predicting fatigue crack initiation in metals using dislocation dynamics simulations

The presented work aims at deepening the understanding of the initiation of fatigue cracks in metals. The work is based on an argument of Mura and Nakasone [1] where an energy criterion is used to predict the initiation of a fatigue crack from a slip band. The discussion is based on the evolution of dislocation networks, as these are the prime cause for permanent deformation in metals. Using high performance computing, 3D dislocation dynamics simulations [2] are performed over several cycles to study the growth of the dislocation arrangement. Then the evolution of energy in the system is determined, including all relevant terms such as: energy of the elastic field of the dislocations and their interaction, core energies, dissipation, energy stored in the continuum and external work. A hypothetical crack is placed in the region of the largest dislocation density and it is checked, if the energies stored in part of the dislocation network should be exchanged with the surface energy of a crack to lower the overall energy state of the system. The size of the crack is based on the number of dislocations that were previously formed in the network, as the motion of these dislocations towards the hypothetically formed free surface would form the actual crack. The presented work requires only minimal input in form of elastic constants and dislocation mobilities (for example from molecular dynamics). Results are presented for different materials (Cu and Mg), grain sizes and loading rates. [1] T. Mura, Y. Nakasone, A Theory of fatigue crack initiation in solids, Journal of Applied Mechanics, 57 (1990) [2] A. Arsenlis, W. Cai, M. Tang, M. Rhee, T. Oppelstrup, G. Hommes, T.G. Pierce, V.V. Bulatov, Enabling strain hardening simulations with dislocation dynamics, Modelling and Simulation in Materials Science and Engineering, 15 (2007

Uncertainty Quantification of Microstructural Properties due to Experimental Variations

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143052/1/6.2017-0815.pd

Utilization of a Linear Solver for Multiscale Design and Optimization of Microstructures

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140693/1/1.j054822.pd

Multiscale Modeling of Oxidative Degradation of C-SiC Composite

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83592/1/AIAA-2010-3059-508.pd