The microstructure of the nacre of abalone seashell (top) and of our ceramic composite (bottom). From the original paper.

While playing around with the freezing behavior of anisotropic objects during the PhD of Florian Bouville, we realize we could use the ice-induced alignement of anisotropic ceramic particles (alumina platelets) to prepare a dense ceramic composite. The structure of the dense material is reminiscent of that of nacre, encountered in some species of seashells, and which is well-known for its damage resistance (did you already tried to open one with a knife?).

Breaking tiny samples to understand the role of the interfacial properties.

Such structures are known as brick-and-mortar materials, and their damage resistance originates in the load redistribution at the crack tip as well as an extensive crack deflection. The damage resistance of this particular composites, made of 98.5% alumina and 1.5% of a glassy phase, is remarkable.

We later demonstrated that a much more classic and scalable processing route based on uniaxial pressing could be used to achieve the same microstructure while being able to prepare much larger samples, with a thickess up to 1cm. We spent a lot of time and effort to try to understand the mechanical properties of these materials, both at small and large scales. It turns out that the macroscopic properties are controlled by the interfacial properties of the composite, which we now need to optimize.

A key parameter to optimize these structures is to achieve a homogeneous distribution of the building blocs, which can be achieved by heteroaggregation.

Crack propagation in ideal (left) and realistic (right) brick and mortar microstructures, by discrete elements modeling.

In parallel, with colleagues from Grenoble, we used discrete elements modelling to understand and optimize the mechanical response of these structures, including modelling on realistic microstructures. The next challenge is now to implement these findings into real materials !