Many materials show micro cracks which influence the behavior of the overall structure. An efficient way to accurately include micro cracks in 3D simulations of structures with considerably larger cracks is enabled. The FE mesh independent of the existing crack path is realized with the XFEM. As the mesh resolution is nevertheless related to the crack length the domain is decomposed into a coarse scale and a fine scale domain using a model indicator. The domains are coupled within the multiscale projection method which includes the micro cracks explicitly on the fine scale and implicitly on the coarse scale. For further improvements a mesh adaptivity scheme based on an error indicator is implemented on both, the coarse and the fine scale. As a result a multiscale simulation with a volume of 56.25 cubic mm and a micro crack surface of 1360 sq. micro meter is modeled