  Composites with high strength and high fracture resistance are desirable for
structural and protective applications. Most composites, however, suffer from
poor damage tolerance and are prone to unpredictable fractures. Understanding
the behavior of materials with an irregular reinforcement phase offers
fundamental guidelines for tailoring their performance. Here, we study the
fracture nucleation and propagation in two phase composites, as a function of
the topology of their irregular microstructures. We use a stochastic algorithm
to design the polymeric reinforcing network, achieving independent control of
topology and geometry of the microstructure. By tuning the local connectivity
of isodense tiles and their assembly into larger structures, we tailor the
mechanical and fracture properties of the architected composites, at the local
and global scale. Finally, combining different reinforcing networks into a
spatially determined meso-scale assembly, we demonstrate how the spatial
propagation of fractures in architected composite materials can be designed and
controlled a priori.
