# Role of Hydrogen Concentration in Strength and Damage of Polycrystalline Iron Under Triaxial Tension

## TL;DR

This paper studies how hydrogen concentration affects the strength and damage of polycrystalline iron under triaxial tension using simulations.

## Contribution

The novel contribution is the systematic investigation of hydrogen's role in void evolution and its coupling with temperature effects.

## Key findings

- Low hydrogen concentrations (≤1%) impede dislocation motion and delay void growth.
- Void volume evolution follows a three-stage pattern: slow, rapid, and decelerated growth.
- High temperatures make temperature the dominant factor in strength, while hydrogen's effect is minimal.

## Abstract

The mechanical response of the iron–hydrogen (Fe-H) system under triaxial tensile loading is systematically investigated using molecular dynamics simulations. The study focuses on how hydrogen concentration affects the stress state and void evolution and further explores its coupled effects with temperature. The results indicate that when the hydrogen concentration is less than or equal to 1%, hydrogen atoms impede dislocation motion, thereby retarding void growth by promoting dislocation entanglement and the formation of loop structures. Moreover, the evolution of void volume exhibits a typical three-stage characteristic: an initial slow growth phase, a rapid growth phase, and a decelerated growth phase after coalescence. In addition, the evolution of void surface area in the model essentially results from competition between two mechanisms: the decrease caused by void collapse and coalescence and the increase caused by void expansion. Cluster configuration analysis reveals that void formation around the clusters serves as a critical turning point for their structural stability, and the subsequent evolution of the voids leads to a substantial reduction in local structural stability. The analysis of the coupling effect between temperature and hydrogen concentration reveals that under high-temperature conditions, temperature plays a key role in determining the strength, while the strengthening effect of low hydrogen concentrations can be neglected. Additionally, at low temperatures, hydrogen concentration has a negligible effect on structure, but under elevated temperatures, increased hydrogen concentration markedly intensifies the degree of structural disorder.