Date of Graduation

Summer 2016

Document Type

Honors Research Project

Degree Name

Bachelor of Science

Major

Applied Mathematics - BS/MS

Research Sponsor

Nao Mimoto

First Reader

Curtis Clemons

Second Reader

Kevin Kreider

Abstract

The objective of this work is to develop a cellular automata based model of pitting initiation and subsequent three-dimensional evolution of pit shapes. Here, a cellular automaton is a collection of cells, each of which may be in one of two states, metallic or electrolyte, arranged over a grid. Pit initiation is implemented over a 2-dimensional grid representative of the metal surface while pit propagation is resolved over a 3-dimensional grid which describes a subsection of the bulk metal. The size of the bulk metal will be on the order of millimeters, and a layer of electrolyte, in which chloride will act as the aggressive anion, will cover the bulk metal. A cell within the automaton may change its state each fixed time interval based on a set of rules, called transition rules. The rules are based upon corrosion mechanisms and are implemented stochastically. Further, parametric analyses are performed to simulate pit damage evolution for a metal electrode in various environments. Results from the model are representative of aluminum alloys relevant to aircraft structures. The initiation scheme is capable of reproducing the number of (meta)stable pitting events per area found in the literature for Aluminum Alloy 7075, and the propagation scheme simulates pit shapes seen in nature, such as subsurface and undercutting pits.

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