Theses and Dissertations
A fully coupled implementation approach to study hydrogen embrittlement in metals using finite element analysis
Mississippi State University
Date of Degree
Dissertation - Campus Access Only
Doctor of Philosophy (Ph.D)
James Worth Bagley College of Engineering
Department of Aerospace Engineering
Diverse hypotheses are behind the strength degradation in metals due to hydrogen diffusion, leading to a severe, sudden failure. These diverse hypotheses of hydrogen embrittlement include various mechanisms that are responsible for the embrittlement of metals due to hydrogen exposure in their microstructures. This research study focuses on one hydrogen embrittlement mechanism: Hydrogen-Enhanced-Localized-Plasticity (HELP). The HELP is the only single mechanism characterized by promoting localization of plastic flow ahead of the crack by increasing dislocation motion in that region. The current state of the art is a development of a numerical model representing a fully diffusion-mechanical coupled model. This fully coupled model attempts to gain valuable insights into hydrogen's influence on the mechanical properties and the fatigue life of metals, in general. First, detailed development of a numerical approach is illustrated describing how to fully couple the hydrogen diffusion and stresses using a finite element method. The formulation is based on a coupled temperature-displacement procedure using Abaqus. This coupled computational model, described in this first part, is novel because the mechanical part is based on an isotropic-kinematic hardening law. Furthermore, this fully coupled numerical model can capture both a hardening and softening effect of the stress-strain curve when the solution of the plastic properties is dependent on hydrogen. This can also contribute in a complementary way to the results previously shown by other researchers. Though these previous studies used the same hydrogen diffusion model, their mechanical part was based on a power law. Second, this research attempts to delve into the hydrogen effect on the constitutive response of metals undergoing a cyclic load. Hence, based on the HELP theory, this constitutive coupled model can capture different cyclic hardening behaviors. This study can largely contribute to understanding the degradation of the mechanical properties of materials before crack propagation, which has been heavily covered in the literature.
Yassir, Sofia, "A fully coupled implementation approach to study hydrogen embrittlement in metals using finite element analysis" (2022). Theses and Dissertations. 5670.