Micromechanics of Hydrogen-Induced Crack Initiation in Pipeline Steels and Subcritical Crack Growth
Dadfarnia, Mohsen
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https://hdl.handle.net/2142/83926
Description
Title
Micromechanics of Hydrogen-Induced Crack Initiation in Pipeline Steels and Subcritical Crack Growth
Author(s)
Dadfarnia, Mohsen
Issue Date
2009
Doctoral Committee Chair(s)
Sofronis, Petros
Department of Study
Mechanical Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Language
eng
Abstract
To further explore the influence of hydrogen on ductile fracture, we model sustained-load cracking in the iron-base superalloy 1N903 at hydrogen pressures at which fracture is governed by plasticity. Through a micromechanics analysis, we quantify the void growth dependence on stress triaxiality and hydrogen-induced material softening as a function of position ahead of a crack tip. Correlation of the calculated void diameters with experimentally measured ones leads to the identification of a microstructural length that characterizes the onset of hydrogen-induced cracking. Lastly, to analyze the mechanics of sustained-load cracking at pressures greater than 100 MPa for which experiments suggest that hydrogen promotes failure by intergranular cracking, we simulate crack propagation by cohesive finite element methodology based on hydrogen-induced decohesion thermodynamics. The results reveal a number of issues related to the complexity of the failure mechanism and the robustness of the cohesive element approach.
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