The freedom of design provided by additive manufacturing enables the fabrication of filigree structures such as strut-based lattices. Strut-based lattices exhibit outstanding mechanical properties and a low density, simultaneously. Therefore, these open-cell structures can be used as cores in sandwich panels. The lightweight advantage of sandwich panels is due to the separation of the high-strength face sheets by a low-density material. However, the difference in the core and face sheet material stiffness and localized loads cause highly localized deformations and stresses, which are not considered in the classical sandwich theories. Moreover, using homogenization methods to model the lattice core does not enable the consideration of local effects. In this work, a computational model is presented, which enables the calculation of localized stresses and deformations in the struts of lattice cores with acceptable computational effort using de-homogenization methods.  To outline the advantage of using additively manufactured strut-based lattices, the strut diameter of the lattice core is varied through the core thickness. Thus, the stress distribution in the graded core can be controlled and adapted through the core thickness.