Computational modelling of hydrogen-induced failure in metallic materials

Date

2024-9-05

Author

Tatlı, Berkehan

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The phenomenon of hydrogen-induced failure, which affects a wide range of metals, has attracted significant interest in recent times. This phenomenon arises when hydrogen particles diffuse and relocate within the lattice structure of metallic materials upon exposure to a hydrogen-producing environment. Literature on hydrogen-induced failure has demonstrated that the existence of hydrogen atoms within the lattice structure of metallic materials profoundly affects both the onset and propagation of cracks, resulting in decreased ductility, strength, toughness, and fatigue life. Several theories have been proposed to explain the various mechanisms involved in hydrogen-induced failure, such as hydrogen-enhanced plasticity and hydrogen-enhanced decohesion. These mechanisms connect hydrogen-induced damage to the interactions occurring between hydrogen and imperfections within the material. Therefore, it is crucial to accurately describe the progression of material defects and migration of hydrogen to comprehend hydrogen-induced failure. In this thesis, a potential-based mixed-mode cohesive zone model is coupled with stress-driven hydrogen transport and constitutive frameworks including isotropic Von Mises plasticity, crystal plasticity, and strain gradient crystal plasticity. This framework is used to model the hydrogen-enhanced decohesion mechanism, focusing on hydrogen-induced intergranular failure as the primary failure mechanism. Initially, 2D Von Mises plasticity simulations are used to validate the proposed novel framework against data from notched specimens, showing a strong correlation with experimental results. Then, crystal plasticity and strain gradient plasticity simulations are conducted on the generated and preprocessed 3D polycrystalline RVEs to examine the size and nonlocal effects in the micromechanical modeling of hydrogen-induced failure.

Subject Keywords

Hydrogen-induced failure, Cohesive zone modeling, Strain gradient crystal plasticity, Size effect, Polycrystalline materials

URI

https://hdl.handle.net/11511/111397

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Graduate School of Natural and Applied Sciences, Thesis