Session: Research Posters

Paper Number: 113462

113462 - A Novel Multi-Scale Model for the Effect of Hydrogen on the Mechanical Behavior of Crystalline Materials 

Hydrogen Embrittlement (HE) poses a serious risk to structural materials because of its well-known influence on the severe degradation in their mechanical properties (e.g. fracture toughness). Hydrogen gas readily diffuses through the surface from a variety of sources (e.g. heat treatment and fabrication processes, in-service exposure to hydrogen-containing gases, and in chemical processing steps). A fraction of surface-absorbed hydrogen diffuses by hopping through interstitial sites in the crystal lattice, while the remainder is trapped at various crystal defects, such as vacancies, dislocations, and grain boundaries. As a result, the interaction between trapped hydrogen and dislocations can drastically influence plastic deformation and failure process in high strength steels. Accordingly, many investigations have been conducted to identify the crucial role of hydrogen on the plastic deformation and failure mechanisms of high-strength steels. 

The precise mechanisms by which the trapped hydrogen solutes impact the plastic deformation and failure of high-strength steels are still under active investigations. For example, solute hydrogen was found to increase both dislocation and cleavage crack velocities, while at the same time decreasing the stacking-fault energy.

Over the past couple of decades, three common embrittlement mechanisms were identified. Hydrogen Enhanced Decohesion Embrittlement (HEDE) theory proposes that hydrogen weakens the atomic bonding at the crack tip leading to the cleavage-like failure process. The hydride-induced embrittlement mechanism can be observed in materials such as niobium and zirconium, where hydrides can be easily formed at stress concentration zones. In systems that do not form hydrides, such as 310s Stainless Steel under mechanical load, the Hydrogen Enhanced Localized Plasticity (HELP) theory is the most widely accepted hypotheses for the influence of hydrogen solutes on dislocations. In this mechanism, hydrogen atmospheres around dislocations can shield their stress field, resulting in smaller interactions between dislocations and other obstacles.

The present work is devoted to constructing a novel physics-based dislocation model that accurately predicts the effect of hydrogen on the mechanical behavior of high-strength steels on multiple scales. Specifically, the model aims at explaining the effects of increased hydrogen concentration on the increase in the flow stress, on the rate of work-hardening, and on the critical concentration at which yield drop is experimentally observed.  The proposed model is based on a set of time-dependent and coupled differential equations for the rates of generation and immobilization of dislocations, including mobile, immobile, and boundary dislocations. Static and dynamic recovery of mobile and immobile dislocations are considered as well. Hydrogen concentration is calculated by considering trapped hydrogen in the dislocation core for both open and closed. The developed model is coupled to the finite element (FE) package ABAQUS through the VUMAT user subroutine to study the effects of HE on typical tensile specimens. Furthermore, the proposed model utilize extensive Molecular Dynamics (MD) simulations to obtain proposed contants in a hierarchical multi-scale approach.

Presenting Author: Tarek Hatem University of Nevada, Las Vegas

Presenting Author Biography: Tarek Hatem

Authors:

Tarek Hatem University of Nevada, Las Vegas