A phase field model for elastic-gradient-plastic solids undergoing hydrogen embrittlement

Philip K. Kristensen, Christian F. Niordson, Emilio Martínez-Pañeda*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

We present a gradient-based theoretical framework for predicting hydrogen assisted fracture in elastic-plastic solids. The novelty of the model lies in the combination of: (i) stress-assisted diffusion of solute species, (ii) strain gradient plasticity, and (iii) a hydrogen-sensitive phase field fracture formulation, inspired by first principles calculations. The theoretical model is numerically implemented using a mixed finite element formulation and several boundary value problems are addressed to gain physical insight and showcase model predictions. The results reveal the critical role of plastic strain gradients in rationalising decohesion-based arguments and capturing the transition to brittle fracture observed in hydrogen-rich environments. Large crack tip stresses are predicted, which in turn raise the hydrogen concentration and reduce the fracture energy. The computation of the steady state fracture toughness as a function of the cohesive strength shows that cleavage fracture can be predicted in otherwise ductile metals using sensible values for the material parameters and the hydrogen concentration. In addition, we compute crack growth resistance curves in a wide variety of scenarios and demonstrate that the model can appropriately capture the sensitivity to: the plastic length scales, the fracture length scale, the loading rate and the hydrogen concentration. Model predictions are also compared with fracture experiments on a modern ultra-high strength steel, AerMet100. A promising agreement is observed with experimental measurements of threshold stress intensity factor Kth over a wide range of applied potentials.

Original languageEnglish
Article number104093
JournalJournal of the Mechanics and Physics of Solids
Volume143
Number of pages23
ISSN0022-5096
DOIs
Publication statusPublished - 2020

Keywords

  • Fracture
  • Hydrogen embrittlement
  • Phase field fracture
  • Strain gradient plasticity
  • Stress-assisted diffusion

Cite this