This study deals with a method to change the space-time scales for multi-domains calculations in explicit dynamics. The interest of such a method inspired by the techniques of mesh refinement [
], is to improve only when necessary the space (and time) discretization of one or more subdomain, during a significant phase of calculation. The method is based on a mesh refinement or coarsening which is activated according to a predefined criterion. Here, the different meshes used for the same domain are defined before the calculation. This is why we will refer to switch or mesh change rather than remeshing. Although this work is a part of researches on multi-domains approaches [
], we will concentrate here on refinement of one of the subdomains omitting the interactions with the other subdomains. After the mesh change, the different mechanical fields associated with the new mesh must be projected from the old mesh and must allow us to continue the calculation on the new mesh. This continuation is correct if the projected fields, associated with the new mesh, satisfy the equilibrium equations as well as possible. The transfer of fields by simple interpolation does not ensure, in general, this condition, in particular for problems with high non-linearities. Moreover, these simple interpolation methods become particularly unstable when used in an dynamic explicit scheme. So, the main difficulty will be to maintain stability and precision of calculation. That is why we will concentrate on the transition step and on the way of equilibrating the solution on the new discretization in the linear and non-linear case (material non-linearity). Finally, the decision to switch from a coarse mesh to a fine mesh is controlled here by a physical criterion based on the maximum plastic strain. Currently the algorithm developed in CASTEM co has been tested on several simple geometries. These first examples allowed us to validate the method and to show its efficiency in the linear and non-linear case.