In this research, the virtual testing approach is used to study the failure of inserts in sandwich structures. First, a reduced F.E. model of inserts is presented, which includes nonlinear aspects of the materials such as the buckling and collapse of the honeycomb cells, the failure of the potting and the matrix failure of the skins. These model are validated through comparison with real tests showing a good agreement. This work is part of the development of an insert sizing method that could be an alternative to the classical analytical methods.