In order to solve efficiently large scale problems arising from the simulation of heterogeneous structures, described up to the microscale, a multiscale computational strategy strongly related to homogenization techniques has been proposed in Ladevèze and Dureisseix, Int. J. for Computational Civil and Structural Engineering 1:18-28, 2000. In this paper, specific tools required to address the case of composite materials are proposed: the use of a third scale and of the periodic media homogenization theory within the areas located far from the boundaries.