Influence of Dissipative Cohesive Zone Law on Hydrogen Embrittlement

Abstract

The dissipative cohesive zone model of Gao was applied with the hydrogen transport model established by Sofronis to approximate a cracked geometry subject to constant load and hydrogen embrittlement. The model assumed small scale yielding, which was realised through modified boundary analysis. The model was implemented in the finite element method software package \verb+Abaqus+ with a user defined material and element. The ligament employed cohesive elements with surface energy equal to 37.125 N/mm. The analyses were mechanically loaded to J = 37.125 N/mm, and kept constant while time dependent hydrogen diffusion diminished the strength of the cohesive elements. Varying the Gao viscosity coefficient while keeping other values constant does not change the time to fracture. Thus mechanical stability can be added without affecting the outcome in a constant load hydrogen diffusion analysis.

This thesis has also explored the numerical aspects of the dissipative cohesive zone model. A combination of analytical solutions and finite element analysis indicates that the implementation of the dissipative cohesive zone model expands the solution space considerably, compared to classical cohesive zone modeling. This results in poor accuracy for models employing dissipative cohesive zone model.