Graded and architected materials can be designed to adapt mechanical properties to the individual use case. For instance, hierarchically structured materials have shown enhanced work of failure and desirable adhesion and detachment properties. This material design is in the range of bionic engineering, as multiple examples of hierarchical microstructure can be found in nature, with examples ranging from bone to the gecko foot [1, 2, 3]. Recent numerical studies have used coarse-grained methods and network simulations to identify the mechanisms by which hierarchical arrangements produce greater resistance to fracture [5, 6, 7] and, in the context of adhesion and detachment, help localize failure precisely at the interface. This advantage comes without losing fracture strength [4]. Our study focuses on fracture in composites, where an architected constituent (hierarchical or graded) is coupled to a heterogeneous substrate. The model employs a scalar elasticity approach coupled with a von-Mises-type failure criterion [4, 8, 9]. While both realizations allow for fracture localisation at the interface, the hierarchically structured composite displays significantly higher fracture toughness. This is due to the ability of the hierarchical gaps to arrest crack propagation. Furthermore, we show the relationship between the spectral properties of the stiffness matrix of these systems, the fracture behaviour and the failure location. REFERENCES [1] P. Fratzl and R. Weinkamer. Nature’s hierarchical materials, Progress in Materials Science (2007) 25 [2] R. Lakes, Materials with structural hierarchy. Nature (1993) 361 [3] H. Gao. Application of fracture mechanics concepts to hierarchical biomechanics of bone and bone-like materials. Advances in Fracture Research: Honour and Plenary Lectures Presented at the 11 th International Conference on Fracture (2006) [4] C. Greff , P. Moretti and M. Zaiser. Tuning load redistribution and damage near heteroge neous interfaces (2024) 14 [5] D. Sen and M. J. Buehler. Structural hierarchies define toughness and defect-tolerance despite simple and mechanically inferior brittle building blocks. Sci. Rep. (2011) 1 [6] R. Mirzaeifar, L. S. Dimas, Z. Qin and M. J. Buehler. Defect-tolerant bioinspired hierar chical composites: Simulation and experiment. ACS Biomater. Sci. Eng. (2015) 295 [7] P. Moretti, B. Dietemann, N. Esfandiary. Avalanche precursors of failure in hierarchical fuse networks. Scientific Report