Local adaptive refinement and multilevel method for the fracture of heterogeneous materials

In order to anticipate effects of ageing in confinement structures of nuclear power plant, the IRSN develops research programs to study the ageing of concrete. A micromechanical approach, based on Cohesive Zone Models, and the 'Eigen-Erosion' method, based on energetics consideration, are used. The aim of this study is to reduce the computational cost while keeping simulations with good accuracy in the areas of interest. The strategy is to adapt the spatial discretization in the areas of interest using local adaptive refinement techniques. The selected refinement method is called CHARMS (Conforming Hierarchical Adaptive Refinement Methods). CHARMS is based on the refinement of basis functions and enables refinement without any loss of the initial mesh quality. The geometrical non-conformities are implicitly handled. Initially applied to Fluid Mechanics, the method is first extended to Solid Mechanics with a specific refinement criterion. It is then applied to 'Eigen-Erosion' and to Cohesive Zone Models. The inclusion's shape of a Representative Elementary Volume of numerical concrete is studied in order to determine the influence over the apparent behaviour and the crack propagation. (author)