Date of Award

Spring 1-1-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Todd Murray

Second Advisor

Andrew J. Slifka

Third Advisor

Robert Amaro

Abstract

The growing government and industry interest in vehicles powered by hydrogen fuel cells has warranted research in recent years on use of the existing oil and natural gas pipeline infrastructure for widespread hydrogen fuel transport. Much of this research aims to assess the mechanical properties of pipeline steel in a hydrogen environment, as they are different from its properties in oil and natural gas. The current research analyzed the effects of 800 psi and 5000 psi environing hydrogen pressures on crack growth rates in acicular ferrite and ferrite pearlite steels when the steels were fatigued at frequencies of 1 Hz and 0.1 Hz at a load ratio of 0.5. A pressure of 800 psi was found to accelerate crack growth for the entirety of the Paris regime observed, and that of 5000 psi further accelerated crack growth in the beginning of the Paris regime. Crack growth rates were not influenced by variations in frequency and microstructure when the environing hydrogen pressure was 5000 psi, but they were faster in acicular ferrite than in ferrite pearlite in 800 psi of hydrogen. The experimentation was supplemented with finite element modeling of fatigue crack growth and stress-driven hydrogen diffusion in steel in ABAQUS. The modeling serves as a proof of concept, and can later be expanded to simulate hydrogen assisted fatigue crack growth. Such a full simulation would enable predictions of hydrogen assisted fatigue crack growth under given operating conditions, along with the derivation of new predictive relationships of hydrogen assisted crack growth based on parameters that are difficult to measure experimentally, such as plastic strain.

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