Abstract
Industrial power generation and transmission structures are designed to have a service life of 40 years. The prediction of damage development is therefore crucial to ensure the safety and reliability of these facilities. As part of the decarbonization of energy sources, hydrogen will play an important role as an energy vector. However, its presence in the material induces premature failure and ductile fractures with reduced ductility and toughness.
The aim of this work is to develop and implement a reliable and efficient strategy to simulate hydrogen embrittlement by the finite element method (FEM) integrating plasticity and damage coupled to hydrogen diffusion. Since damage is highly dependent on local stresses and hydrostatic pressure, mixed formulations in displacement, pressure and volume variation have been proposed to control volumetric locking. Using these elements, the hydrostatic stress is a nodal variable so that it becomes straightforward to compute its gradient, which strongly influences hydrogen diffusion towards highly stressed areas.
The Gurson-Tvergaard-Needleman (GTN) is considered to model the ductile rupture, which has proven to be capable of predicting phenomena such as "cup and cone" failure. Such a model leads to spurious damage and strain localization (and mesh dependence). To solve this problem and to account for interactions between neighboring material points, a nonlocal FE formulation is used to regularize strain/damage localization. It is based on an implicit gradient nonlocal model with two internal lengths (applied to plastic volume variation and accumulated plastic strain). The model allows regularizing void growth, strain controlled nucleation. Mesh size and orientation independence is achieved for sufficiently fine meshes. All the implementations and simulations have been done using the Z-set software.