Strain gradient plasticity modeling of hydrogen diffusion to the crack tip

TL;DR

This paper models hydrogen diffusion to crack tips considering strain gradient plasticity, revealing the significant role of geometrically necessary dislocations in hydrogen transport and embrittlement.

Contribution

It introduces a strain gradient plasticity approach to accurately predict hydrogen diffusion and crack tip behavior, improving upon conventional plasticity models.

Findings

GNDs significantly influence hydrogen transport near cracks.

SGP models align well with experimental deformation data.

High hydrogen concentrations are predicted close to crack tips.

Abstract

In this work hydrogen diffusion towards the fracture process zone is examined accounting for local hardening due to geometrically necessary dislocations (GNDs) by means of strain gradient plasticity (SGP). Finite element computations are performed within the finite deformation theory to characterize the gradient-enhanced stress elevation and subsequent diffusion of hydrogen towards the crack tip. Results reveal that GNDs, absent in conventional plasticity predictions, play a fundamental role on hydrogen transport ahead of a crack. SGP estimations provide a good agreement with experimental measurements of crack tip deformation and high levels of lattice hydrogen concentration are predicted within microns to the crack tip. The important implications of the results in the understanding of hydrogen embrittlement mechanisms are thoroughly discussed.