Date of Graduation

5-2016

Document Type

Thesis

Degree Name

Bachelor of Science in Mechanical Engineering

Degree Level

Undergraduate

Department

Mechanical Engineering

Advisor/Mentor

Spearot, Douglas E.

Committee Member

Nair, Arun

Second Committee Member

Zou, Min

Abstract

Hydrogen embrittlement is a main factor in the premature failure of metals under stress. Using molecular dynamics (MD) simulations, two models were built in order to study how the presence of hydrogen at interstitial positions within the nickel lattice affects how it fractures. The first model was a 3D single crystal nickel sample, while the other was the same nickel model but with different concentrations and locations of hydrogen positioned at or near the crack tip. Two aspects of fracture were studied and compared between the different simulations: the crack tip velocity and dislocation nucleation from the crack tip. Analysis of the simulations shows that different concentrations of hydrogen effect both aspects of fracture in nickel, while the size of the region containing hydrogen has no influence whatsoever. The crack growth initially accelerates when there is hydrogen in the system, indicating that the hydrogen enhanced decohesion (HEDE) mechanism is acting. An increase in dislocation nucleation at the crack tip is caused by the action of the hydrogen enhanced localized plasticity (HELP) mechanism.

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