The nacreous layer of mollusk shells holds design concepts that can effectively enhance the fracture resistance of lightweight brittle materials. Mineral bridges are known to increase the fracture resistance of nacre-inspired materials, but their role has been difficult to quantify. The challenge has been to isolate and control mineral bridge connectivity in a model composite with microstructures on the same scale as the biological material. In this study, we fabricate these tunable nacre-like composites from highly aligned alumina platelets, interconnected by titania mineral bridges and infiltrated with epoxy matrix phase, and experimentally quantify the influence of mineral bridge density on the fracture properties. Mineral bridge density from image analysis of composite cross sections was correlated with the fracture behavior in mechanical tests and a quantitative model was developed using the insight that shear lag describes the stress transfer through the mineral phase. This model quantitatively describes the relationship between the fracture strength of the composite, platelet strength, and mineral bridge density, which provides powerful guidelines for the design of lightweight brittle materials with enhanced fracture resistance. We illustrate this potential by fabricating nacre-like bulk composites with unparalleled fracture strength, 20% stronger than the previously reported materials.

Researchers produce inorganic scaffolds using magnetic assembly to align preformed heterogeneous ceramic bricks, which are hot-pressed and infiltrated with an organic phase to generate a strong and tough composite that has a nacre-like brick-andmortar structure, interconnected with submicron interplatelet mineral bridges. The pioneering aspect of this study is the use of alumina platelets that are precoated with a ceramic layer that sinters at a lower temperature compared to the sintering temperature of the alumina platelets. Using precoated alumina platelets significantly minimize the processing time and material heterogeneity, which are commonly observed in fabrication processes that rely in co-sedimentation of particles exhibiting different size and density.