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Description
The presence of hydrogen in steels leads to a significant loss of ductility, giving rise to a ductile to brittle transition with increasing hydrogen concentration, which is a major concern in the safety assessment of structural components. Among other effects, the hydrogen-enhanced decohesion (HEDE) and the hydrogen-enhanced localized plasticity (HELP) mechanisms are primarily associated with this ductile to brittle transition [M.B. Djukic, et al., Eng. Fract. Mech., 2019, 216:106528].In the current contribution, a monolithically coupled chemo-mechanics framework is presented that incorporates both the transient diffusion of hydrogen and the gradient-extended nonlocal Gurson-Tvergaard-Needleman (GTN) damage model [O. El Khatib, et al., Int. J. Fract., 2023, 241:73-94]. As the framework is inspired by a rate-type variational principle, the diffusion problem is formulated in terms of the chemical potential, which naturally accounts for the influence of the stress on the species flux. Thus, the tedious computation of the gradient of the hydrostatic stress by means of the projection of quadrature point values and shape function derivatives is completely avoided. Furthermore, the influence of hydrogen on the porosity evolution is included in the nonlocal GTN model by linear scaling functions as proposed in [R. Depraetere, et al., Comp Mater Sci, 2019, 200:110857]. The implementation of the model as a user element (UEL) in Abaqus and in particular the return mapping based on an Augmented Lagrangian formulation will be discussed in detail. In addition, representative boundary value problems illustrate the ability of the proposed, phenomenological model to describe the upper shelf of the hydrogen-induced ductile to brittle transition.
