Ductile fracture modelling using local approaches, application to steel welded joints in nuclear components

International audienceThe simulation of crack propagation in ductile materials using the finite element method requires appropriate models for describing the nucleation, growth and coalescence of voids in a robust way. Local models, such as Rousselier and Gurson-Tvergaard-Needleman are now available in the finite element softwares as Cast3m [3]. A large number of models of this kind can be found in the literature, but they suffer from numerical drawbacks. First, they often show a marked mesh dependency of the solution. Second, volumetric locking of the elements is common in elastoplastic damage models in near-incompressible conditions. These two major issues must be solved in order to insure the robustness of such approaches. Our goal is to propose a model which be able to handle these two problems. The mesh dependency can solved by using regularization techniques, such as implicit gradient enrichment of an internal variable [1]. The locking can be treated, either using selective integration techniques, or a mixed formulation [2], which adds the volume variation as a new variable in addition to the displacement.The proposed models, based on the existing Rousselier and GTN models in Cast3m [3], address both issues using an implicit-enriched gradient of damage, and include a mixed formulation in the local models to ensure the desired robustness. In this presentation, the new models and the implementation of the new models are first presented. In a second part, simulations of crack propagation using the proposed models for axisymmetric and compact-tensile specimens in 2D using the Cast3m finite element software [3] are used to illustrate the relevancy of the approach