Micromechanics of Hydrogen-Induced Crack Initiation in Pipeline Steels and Subcritical Crack Growth
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.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign