Neutron Imaging and Constitutive Modeling of Hydrogen Embrittlement in Steels

Abstract

This thesis concerns the phenomenon of coupled hydrogen diffusion and fracture in steels from both experimental and computational perspectives. Hydrogen embrittlement, where the ingress of hydrogen (H) reduces a steel’s load-carrying capacity, is a long-standing scientific challenge, first documented in the late 19th century. W.H. Johnson observed that exposing pure iron to an acidic solution led to premature fracture and that the metal regained its original strength and ductility after being removed from the solution for a period. Despite more than a century of research, the mechanistic understanding of hydrogen embrittlement remains limited, primarily because of the multiscale nature of hydrogen behavior and its complex interactions with metallic microstructures. Hydrogen diffuses through thecrystal lattice and interacts with grain boundaries, carbides, voids, cracks, and dislocations. Under external mechanical loading, hydrogen transport is further influenced by dilatational lattice distortions and by moving dislocations, adding additional complexity. As a result, Fick’s law often fails to describe hydrogen diffusion in these systems accurately, and experimental investigations on the submicrometer, micrometer, and engineering scales remain challenging. This thesis addresses these challenges by combining fracture mechanics experiments with neutron imaging to investigate crack propagation caused by hydrogen embrittlement. Additionally, it presents a detailed numerical framework for modeling hydrogen embrittlement at the continuum scale. The strong coupling between mechanical fields and solute concentration necessitates advanced numerical techniques to solve the governing partial differential equations reliably and efficiently

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