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

Abstract : The 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.