Compared to metals and polymers, ceramics are great candidates for applications involving extreme environments like high temperatures, radiations, humidity, or corrosion. However, their poor resistance to fracture propagation greatly limits their use in high-performance structural applications. To this day, the key mechanisms highlighted to improve ceramics’ resistance to crack growth mostly reside in a fine control of the microstructure. This includes reinforcing a bulk matrix with fibres and fillers to bridge a crack or adding features that resist progression ahead of the crack tip such as residual compressive stresses and transformation toughening. On the other hand, millions of years of evolution have gifted natural materials with sophisticated hierarchical structures that enable them to resist fracture propagation despite being primarily composed of brittle ceramics. Among these materials, nacre stands out as having one of the simplest microstructures, resembling a brick-and-mortar wall, yet exhibiting many toughening mechanisms leading to a pseudo-ductile behaviour in tension. Taking inspiration from nacre, many processes and compositions have been developed to produce tough ceramic-based composites. Using the current standards of fracture mechanics, it has been proven that nacre-like composites exhibit higher values of fracture toughness and improved crack-resistance curves compared to bulk ceramics. 
However, characterizing fracture in such materials that exhibit high degrees of deflection and branching remain a challenge, and understanding the link between the microstructure and the crack resistance is necessary to improve these materials further. We have worked on characterizing fracture propagation in nacre-like ceramics composed of alumina bricks and various ceramic interfaces, with the aim of determining the role of the microstructure and composition on the fracture response. To this end, we have developed analytical tools validated by finite element analysis to measure crack resistance curves of highly deflected and branched cracks. Supported by these tools and in-situ synchrotron tomography fracture testing, we assessed the stress intensity mode-mixity at the crack tip as well as quantify the evolution of damage in 3D. This analysis reveals that the stress intensity in mode I and II at the tip of the deflected cracks are almost equal in magnitude and that there are additional reinforcements, probably crack bridging, that further slow down the cracks advance. We finally used a Wedge Splitting technique to link the toughness of the interface and the size of brick-and-mortar structure with the crack deflection observed.